Loki Laufeyson (Marvel Cinematic Universe)/Synopsis

Thor
Loki first appears as a young boy along with his brother Thor as Odin recounts the story of how the Asgardians battled the Jotuns. The story then moves further in time to the present, where Loki is present at Thor's coronation that is interrupted by Jotuns intruding into Asgard. In the wake of this, Thor is eager to launch a counter-attack against the Jotuns, but is ordered by Odin not to pursue his course of action.

Later, Loki finds Thor after the latter throws a tantrum over their father's order not to move against Jotunheim, and he appears to attempt to dissuade his brother while possibly actually goading him into action. On leaving along with Thor, Sif and the Warriors Three, Loki leaves word with a guard to inform Odin of their departure, although whether this is out of concern for their safety or desire to make Thor lose favor with Odin is unclear.

Once in Jotunheim, Thor leads himself and his companions into a violent conflict with the Jotuns even after being granted safe passage home by Laufey. During the ensuing fight, Loki uses his abilities to save his brother and friends in several instances, including creating false versions of himself and hurling magic daggers at the Jotuns. He is attacked by a Jotun that grabs him by the wrist, only to watch his flesh turn Jotun blue before returning to Asgardian color.

After Odin arrives and takes the group back to Asgard after Laufey promises that Thor will have the war and death he desires, Loki stands and watches as his father and brother exchange heated words and insult until Odin, saddened by Thor's arrogance and lack of wisdom, decides to punish him. Loki then tries to intercede on his brother's behalf, only to be given a stern reprimand by Odin and fall silent. Odin banishes Thor to Midgard (Earth) while Loki watches in horror; Odin also sends Thor's hammer Mjolnir, enchanting it to only allow a worthy person to lift it and acquire the Power of Thor.

Loki, Sif and the Warriors Three go to the healing room to treat their wounds. Still wondering about the changing of his flesh on Jotunheim, Loki decides to see if he can induce it by touching the Casket of Ancient Winters in Odin's vault. When he lifts the Casket, his skin up to his hairline turns Jotun blue and his eyes turn Jotun red. He is then interrupted by Odin, whom he confronts about his true origins. Loki then learns that, after the final battle between Asgard and Jotunheim, Odin discovered him as an infant left to die in the Jotuns' temple, and that he is Laufey's son.

At Loki's heated insistence, Odin also reveals that his purpose in rescuing him was not solely out of compassion, but also in the hopes that peace could be brought permanently through Loki, although he then states that those plans no longer matter. Infuriated that he has been lied to and taunted with the promise of a possible birthright, Loki shouts hatefully at Odin who, overwhelmed by the stress of his family falling apart and the impending war with the Jotuns, falls into the Odinsleep in front of him. Loki then cries for the guards for help.

With Thor banished to Earth, Loki is offered the throne by Frigga, and he thus assumes the role of Asgard's regent. From his position of power, he travels briefly to Midgard to lie to Thor (who had been captured by SHIELD), telling him their father had died and that their mother forbids his return, as well as trying unsuccessfully to take Mjolnir for himself. Loki then visits Jotunheim under the guise of trying to repair the damage his brother caused, but instead offers Laufey a chance to slay Odin while he's in the Odinsleep, promising to return the Casket to him in return; Laufey accepts the offer. This exchange also reveals that Loki, admittedly jealous of his adoptive brother and anxious about a kingdom ruled by the loud and violent God of Thunder, allowed several Jotuns to enter Asgard during Thor's coronation as "just a bit of fun" to ruin his brother's special day and to keep Asgard from his reign for a short while longer.

When Sif and the Warriors Three disobey Loki's command to wait for his word by going to Midgard to retrieve Thor, Loki confronts and freezes Heimdall for allowing them to leave. He then sends the Destroyer after them to eliminate everything in its path and prevent Thor from returning home. This action proves to be Loki's undoing when Thor's courage in confronting the Destroyer paves the way for his return, and just as Loki betrayed and killed Laufey in Odin's chamber, Thor arrives to challenge him over his actions. He tries to reason with Loki, but Loki brushes his attempts aside and threatens to attack Jane Foster - with whom Thor has developed feelings - deliberately provoking Thor into attacking him. An intense fight erupts between them in which they both seem evenly matched, but the duel quickly moves to Heimdall's Observatory where Loki had connected the Bifrost to Jotunheim, threatening to destroy it. Thor's power ultimately overpowers Loki's cunning, at the cost of the Observatory and the Bifrost.

As Loki falls into the abyss below, the spear in his hand is grabbed by Thor who, in turn, is anchored to the remnants of the bridge by the newly-awakened Odin. Loki appeals to his adoptive father that, by annihilating the Jotuns, he was doing what was best for Asgard. Odin sadly rejects this and, with his Asgardian life now in tatters, Loki releases the spear and allows the wormhole created by the Bifrost's energy to claim him.

The trickster was not so easily felled, however, and sometime later, an apparition of himself appeared on Earth, where he began to influence Dr. Erik Selvig, who had been summoned by SHIELD to turn his scientific knowledge to the task of unlocking the secrets of the Tesseract, which would supposedly be the key to unlimited sustainable energy for Earth. Loki's apparition whispers words of encouragement to proceed.

The Avengers
Loki returns as the main antagonist of The Avengers, having become an ally of Thanos and in command of a vast alien army known as the Chitauri. After falling through the wormhole at the end of Thor, Loki arrived in a part of the universe unknown to both the Asgardians and humans, and came into contact with The Other, a servant of Thanos who offered a pact that would allow Loki to become Earth's ruler while Thanos and the Chitauri takes the Tesseract. Thanos gives him ancient knowledge through the powers of the Tesseract, providing him with a golden, bladed staff with a blue gem that is powered by the Tesseract itself (which was later revealed to contain the Mind Stone); this staff acts as a very powerful weapon and also as a mind control device, bending those who are touched by the gem's power to its will.

After accepting the deal, Loki turns his focus back to Earth in search of a suitable agent, someone close to the Tesseract. He found Selvig, a friend of Thor's and a renowned astrophysicist who had been recruited by SHIELD to unlock the secrets of the Tesseract. In time, Selvig came to understand some of the Tesseract's capabilities, and through Loki's influence, he developed equipment that would focus some of that power. When the time was right, Loki activated the Tesseract, forming a temporary portal that pulled him through to its location on Earth. He was immediately confronted by SHIELD agents, who fire at him, only to learn that bullets bounced off of his body. SHIELD Director Nick Fury attempts to keep him away from the Tesseract, but Loki manages to use the scepter to subjugate and control Clint Barton/Hawkeye and Selvig, as well as a number of other agents by placing the tip of the scepter at their chest near their heart and allowing the power of the gem to overtake them. He then explains to Fury that he wants the Tesseract as part of his "glorious purpose" which was to free humanity from "freedom...life's great lie" as their one supreme king.

Fury tries to flee with the Tesseract, but then decides to stay and allow himself to die with the Tesseract if it means stopping Loki. However, Selvig and Hawkeye inform Loki of Fury's intent, prompting Loki to gather the turned agents and leave with the Tesseract after attempting to kill Fury, avoiding Maria Hill's attempt to stop them. The energy it has unleashed consumes the area and the entire SHIELD compound with it.

After securing an area to determine the next course of action for the Tesseract, Loki notices that the scepter's gem is glowing and calling out to him. He then allows himself to enter a trance where he appears to The Other in a metaphysical form. The Other warns Loki that, if he fails in his pursuit of Earth and the Tesseract doesn't fall into their hands to be given to Thanos, there will be no place for him to hide from the overlord's wrath and that he will beg for something as sweet as pain.

Unsettled about potential failure and more determined than ever, Loki goes to Stuttgart, Germany with Barton and other turned agents in order to retrieve iridium, a necessary ingredient to stabilize the portal. He disrupts a gala at a large museum while Barton raids a secure installation for iridium. Loki strikes terror into the hearts of patrons and guests by securing the one thing needed for Barton to breach the iridium lock's security measures: the curator's eyeball. He then strides out after the screaming crowd into the streets where he makes several copies of himself, trapping the people and demanding that they kneel before him.

Loki brags that this is mankind's purpose, but a single, elderly man challenges him and his intentions. When Loki prepares to kill the old man, Captain America appears and challenges him. Seconds later, the Quinjet, piloted by Natasha Romanoff, challenges him from the sky. After a brief battle with the super-soldier, during which Loki has the upper hand, Iron Man arrives and threatens to fire upon Loki, daring him to make a move. Outnumbered, Loki allows himself to be captured, secretly plotting to use this to his advantage.

As they journeyed to the SHIELD Helicarrier, Thor arrives and extracts Loki from the Quinjet. After landing on a mountain, Thor attempts to reason with Loki, imploring him to remember that they were brothers (even if not by blood) and to return home to Asgard and surrender the Tesseract. Loki, however, still resents his brother and refuses to cooperate. Thor is then tackled by Iron Man before he can say any more, and Loki remains on his perch as he watches them battle before agreeing to ally themselves. They take Loki to the Helicarrier, where he is placed inside a confinement capsule designed to hold the Hulk. Loki taunts Fury about his attempts to control the Tesseract and his gathering of misfits to defend Earth.

Loki's mere presence is enough to provide a disruptive element that fragments the only group of heroes that had any hope of stopping him. When Black Widow arrived to speak with him, apparently to offer a deal in exchange for Barton's freedom, Loki subjected her to a play of wits where he ferreted out her deeper misgivings, but is completely caught off-guard when she tricks him into revealing that there is already a monster among them and that it is not him. From this, she concludes that the monster is Dr. Bruce Banner and that Loki is planning to use the Hulk to destroy the ship and the heroes as well.

However, Loki's plan to use the Hulk, which is only one aspect of his real intentions, did follow through as another jet carrying Hawkeye and the rogue agents came to his aid, following a signal from the scepter. The wounded Banner transformed into the Hulk, destroying much of the Helicarrier, while one of Loki's controlled agents freed him from the cell. Loki then uses illusions of himself to trick Thor into entering the cell and to distract Agent Phil Coulson. Loki mortally wounds Coulson with the scepter and ejects Thor's cell from the Helicarrier. Though Loki retrieved his scepter, Hawkeye is released from its influence, and Loki heads to New York, where Selvig waits with the Tesseract at Stark Tower.

Loki prepares to welcome his army and begin his glorious, but brief, war on Earth. Tony Stark, still alive after the raid and having figured out Loki's plan, catches up with Loki at Stark Tower and abandons his wrecked Iron Man suit to threaten him. Loki quickly grows weary of Tony's threats and tries to subjugate him with the scepter, only to be physically blocked by the arc reactor in Tony's chest. Annoyed (especially after Stark makes a wisecrack about his "performance issues"), he throws the inventor out of a window, and is surprised when a new Iron Man suit rockets out after the man. Loki then finds himself briefly under attack when Stark, now wearing the new Iron Man armor, rocketed back up to retaliate before the Tesseract opens the portal, allowing the Chitauri to come through and begin their assault.

With his triumph near at hand, Loki walks outside to observe the destruction, only to be confronted by Thor, who demands that he deactivate the Tesseract. Loki refuses, claiming that nothing can stop his war. The two brothers then fight a second time, Loki's scepter matching Thor's hammer. When the confrontation comes to stalemate, Thor urges Loki to look at the destruction he's causing, asking if he truly believes it will end with his rule. While Loki is unsure of himself, his eyes temporarily revert to their normal green color as he claims it's too late to stop the madness. He then briefly considers Thor's appeal to work together to end it all and redeem himself, but the Tesseract's influence over his mind proves stronger than his guilt and he instead stabs Thor with a throwing knife, preparing to strike him down as he kneels before him and laughing in amusement at the sentiment. This only enrages Thor, who disarms Loki, picks him up, and slams him down hard on the ruined balcony.

Loki then throws himself off the building as he is defeated and lands on a small Chitauri flying craft. From there, he leads the attack on the city. When the first of the Chitauri's massive Leviathans is destroyed by the Hulk, Loki commands the Chitauri on the other side of the portal to send the rest of their armada, overwhelming the city's defenses.

Following an aerial chase in which his flying craft is destroyed by one of Hawkeye's arrows, Loki lands back inside Stark Tower, where the Hulk confronts him. Loki then gets to his feet and launches into a frustrated rant that only goads the Hulk into simply grabbing him and repeatedly slamming him into the ground. Afterward the Hulk's attack, Loki is too stunned to fight or threaten any longer, more wounded physically than he had ever been before. When he eventually summoned the strength to crawl, Loki found himself face-to-face with the six Avengers who had defeated the Chitauri and closed the portal. He then quietly requested the drink that Stark had offered him earlier.

After the Tesseract was relinquished to Thor, Loki was bound and placed in a metal muzzle (likely to prevent pleading, threatening, or perhaps use of magic) and led to an open area in Central Park with his brother. From there, Thor used the power of the Tesseract to transport the both of them home to Asgard.

Thor: The Dark World
Loki returns as an anti-hero in Thor: The Dark World. Continuing from The Avengers, he is taken back to Asgard and brought before Odin to answer for his crimes. While Frigga is more than relieved to see him alive, Odin is disappointed in his adopted son. Loki shows no sign of remorse, thinking he committed a benevolent act as a god. Odin thinks otherwise and adds that, if it weren't for Frigga's compassion, Loki would probably be executed. Odin then sentences Loki to spend the rest of his days in the dungeon.

While Loki dwells within confinement, he watches from his cell as Fandral and Volstagg bring in some prisoners, including a disguised Algrim. Loki is visited by Frigga, in the form of a hologram, and expresses her concern toward him. He still has deep compassion for his mother, though he brushes it off, becoming further doubtful of his family's acceptance of him.

When Algrim, who turns into Kurse, causes a prison break, Loki's cell is left untouched by the Dark Elf, but Loki does give advice to Kurse on how to sabotage Asgard's defenses. The imprisoned god then returns to his boredom, but is then informed by a guard that Frigga has been killed in the Dark Elves' attack, evidently causing despair for Loki, as he nearly destroys everything in his cell in a fit of grief and rage. It is not until later on that Thor eventually comes to Loki and sees the effect that Frigga's death has upon him. Thor then offers Loki his freedom in exchange for aid against Malekith, in order to enact vengeance for their mother. Loki knows that Thor is desperate to come seek help from him, though Thor believes that the man he once called his brother is still in Loki. He agrees to help Thor in using diversion tactics. When they meet with Jane Foster (the current host of the Aether) and Sif, Jane slaps Loki for his attack on New York. Sif also promises to kill Loki if he betrays them. With the aid of his allies, Thor, Loki and Jane escape into the crashed Dark Elf ship. Asgardian warriors chase after them until they hop out of the ship and onto a smaller craft flown by Fandral. As he lets the trio make their way out, Loki uses a hidden passageway within Asgard to get to Svartalfheim, home of the Dark Elves.

Once they arrive, Loki betrays Thor by stabbing him and then slices off his hand to prevent him from summoning Mjolnir. He then throws Jane before the Dark Elves, claiming his allegiance with them to spite Asgard. Malekith begins to transfer the Aether within Jane to himself. However, the process is interrupted by Thor and it is revealed that Loki's betrayal was all an illusion to allow Thor to attack unexpectedly. Thor then uses Mjolnir to destroy the gathering Aether with lightning; unfortunately, as the Aether cannot be destroyed, the substance quickly reforms and completes its transfer into Malekith. Malekith and the Dark Elves then make their way toward their giant vessel as Thor attacks them. Kurse throws one of their vortex weapons in the air, which almost catches Jane but Loki pushes her away from it and is nearly sucked in until Thor pulls him away. Thor then fights back against Kurse, but Kurse brutally beats him down. When Kurse moves to kill Thor, Loki stabbed Kurse from behind with a sword. However, the sword proves ineffective on Kurse, who then grabs Loki, impales him with the sword, and throws him to the ground. While Kurse gloats in his victory, Loki declares "See you in Hel, monster" as Kurse quickly realizes that the blade is attached to his own vortex weapon, destroying him before he can react.

As Loki lays dying, Thor clutches his brother in his arms, calming him down and vowing to tell Odin about Loki's selfless deed, but it is too late; Loki replies to Thor, "I didn't do it for him" before closing his eyes and quietly dies as his skin returns to its blue Frost Giant form. A grief-stricken Thor is left to mourn for Loki's sacrifice.

However, after Thor and Jane depart for Earth, Loki awakens, confirming his death to be false, and disguises himself as a warrior. He returns to Asgard to tell Odin that Thor had disappeared with his hammer left behind, and reports to Odin that Loki's body has been found.

After Thor defeats Malekith, Thor returns to Asgard and declines Odin's offer to take the throne while telling Odin of Loki's sacrifice. He offers Mjolnir to Odin, but he tells him it belongs to him if he be worthy of it. Thor thanks Odin and walks away. As he leaves, Odin's image shape-shifts into none other than Loki ,who faked his death. Now seated in the throne he had long desired, he quietly answers, "No. Thank you."

Captain America: The Winter Soldier
Loki does not actually appear in The Winter Soldier, but he is indirectly mentioned, where it was revealed that, thanks to HYDRA's infiltration of S.H.I.E.L.D., Loki's Chitauri Scepter comes under the possession of a faction of HYDRA led by Baron Wolfgang Von Strucker, viewing its properties as beneficial enough to HYDRA's goals that they were willing to deliberately let the various cells in HYDRA be taken down after they were exposed.

Avengers: Age of Ultron
Loki doesn't appear, nor is mentioned in Avengers: Age of Ultron, but it was revealed that his scepter holds an Infinity Stone known as the Mind Stone, which would explain how he was able to brainwash others into his control. The malevolent cyborg known as Ultron stole Loki's scepter after killing von Strucker and taking over his fortress, later using it to brainwash Helen Cho into creating a synthetic body. Ultron would later break the scepter to claim the Mind Stone for himself, though it ends up in the control of the synthetic body, dubbing himself as the superhero Vision. Following Ultron's defeat, Vision uses the Infinity Stone to destroy Ultron's last body.

Doctor Strange
In the mid-credits scene, Thor meets with sorcerer Stephen Strange to discuss Loki, and requests his help in locating the missing Odin, suggesting that Loki didn't actually kill him as initially suspected. Strange accepts, as he doesn't want Loki to stay on Earth any longer than he has to. Loki is not physically present during this scene.

Thor: Ragnarok
Loki returns in the third Thor film as the deuteragonist while the main antagonist role is given to Hela. Loki is first seen in this film in his Odin guise enjoying a play of his faked death during the events of ''The Dark World. ''Thor returns to Asgard to demand that Loki returns to his real form while waving Mjolnir into the air. When Skurge the Executioner shows up, Thor demands to Loki that he takes him to where Odin really is. Skurge teleports the two to New York where Loki banished Odin at a demolished retirement home. Loki is then seen falling through limbo thanks to Doctor Strange. He then shows up in the Sanctum Sanctorum after falling for 30 minutes. After prepping for a fight with Strange, he teleports the two to Norway where Odin is kept. After watching Odin die, both he and Thor fight Hela, who banishes them to Sakaar. Loki is then seen among the crowd in the presence of the Grandmaster.

When the Grandmaster announces a gladiator match, Loki immediately recognizes the champion as the Hulk. After a while, Thor, Banner and Valkyrie approach him due to a peace offering by Valkyrie. Loki agrees to help Thor stop Hela and is instantly left behind on Sakaar. Loki is then approached by Korg to go with him and his fellow gladiators to Asgard. Loki is then seen fighting off the Berserkers while helping the escaping Asgardians. When Thor announces his plan to stop Hela, Loki goes into the Treasure Vault and retrieves the Crown of Surtur and places it into the Eternal Flame. Loki then escapes with everyone else as Surtur destroys Asgard. Later, Loki makes up with Thor, who instantly forgives him for his past evil deeds and is then seen as Thor is crowned king. In a post credit scene, Loki asks if its a good idea to go back to Earth as a massive space ship arrives in front of them.

Avengers: Infinity War
He will appear in Avengers: Infinity War and its untitled sequel, presumably as an antagonist or anti-hero.