Thanos (Marvel Cinematic Universe)/Synopsis

The story of the Mad Titan Thanos from the Marvel Cinematic Universe.

Origins
Thanos was born on a planet called Titan to an unnamed species of large purple life-forms, which was nearing destruction to overpopulation and rapid depletion of resources taking place at the time. Desiring to do something about it, as he deeply cared for his people even though he was viewed as a deformed freak by the rest of his species, he made a proposal to the Titan government that they exterminate half the planet's population so the other could survive. However, they all rejected this idea and called him mad for this. Not too long after, Thanos' species went extinct. Being the only known survivor, Thanos started looking throughout the universe for "balance", but everywhere he went had something wrong with it (at least in his eyes); he took the title of "Mad Titan" and started going planet-to-planet, wiping out half of it to save the other half. In his mind, life was spreading throughout the universe unchecked which would bring ruin.

Among the species, he wiped out was the Zehoberei, a species of green humanoids, and took in the last known survivor Gamora, raising her as his daughter. Also taken in was Nebula, a blue humanoid from another world he visited and had both of them given cybernetic implants. Both Nebula and Gamora had a sibling rivalry but became attached, with Nebula saying "of all our siblings, I hated you the least", suggesting that there were many other siblings. Thanos once calls Gamora "my favorite daughter" without considering Nebula being present at the moment. In their childhood, they would fight a lot, and Thanos would force a cybernetic enhancement on the loser. Each and every time, Nebula would lose and her body became less and less organic. At some point, he took command of the Chitauri species and used their supposed leader The Other as an emissary.

He eventually learned of a way to bring "balance" to the entire universe all at once: the Infinity Stone of immeasurable power. Using a golden gauntlet called the "Infinity Gauntlet", he sought to attach all the Stones to it and wipe out half the universe's populace with the snap of his fingers. At some point, he obtained the Mind Stone (which could mind-control people) and put it into a Chitauri scepter of his making; however, the other Stones eluded him.

The Avengers
In the film, Thanos appears in a post-credits scene, where the Other tells Thanos that the Tesseract, the Space Stone, is in a small world, a human world. It also informs him that Loki is ready to lead the Chitauri, and so he was given the scepter with the Mind Stone to go get the Tesseract. In a post-credits scene, Thanos is revealed to have been Loki's benefactor, having provided the Chitauri Army and the Mind Stone inside Loki's scepter used by Loki in his attempted invasion of Earth. When advised by the Other that opposing the Avengers would be "to court death", as the human race was not as weak as Loki claimed, Thanos glances at the camera and flashes an evil grin.

Guardians of the Galaxy
Thanos plays a more active role in the film, where he has enlisted the help of Ronan, Korath, and his daughters, Gamora and Nebula, to retrieve the Orb (Power Stone) for him. As it turns out, Gamora is not actually Thanos's daughter, since Thanos killed Gamora's family and snatched her as an infant to train her into the perfect assassin, having abused and tormented her in the process of doing so. This causes Gamora to betray Thanos, which leads to a chain of events that leads to Gamora finding her true calling as a protector of the universe and a member of the Guardians of the Galaxy.

When Ronan and Nebula are called to discuss Gamora's betrayal, Ronan kills The Other, who was speaking for Thanos. Thanos does not react to this but is furious at Ronan for not obtaining the Orb (and for apparently alienating Gamora).

After berating Ronan and calling him "Boy", Thanos says he will destroy Xandar for Ronan if he brings him the Orb but promises to "bathe the star-ways with [his] blood" should he fail him. Nebula then easily persuaded the frightened Ronan to leave, as they knew too well he is no match for Thanos.

Thanos promised Ronan that he will help Ronan destroy Xandar in exchange for Ronan's services. However, once Ronan gets a hold of the Orb, he feels he no longer needs Thanos help and also decides to betray him. Nebula also decides to betray Thanos out of jealousy over Thanos showing a preference for Gamora over her. Ronan and Nebula take Korath with them, while Thanos, unfazed by their threats of killing him, cut off contact with them in anger of their betrayal.

In the end, Ronan and Korath are killed by the Guardians of the Galaxy (including Gamora), Nebula escapes and becomes a renegade villain independent of Thanos, and the Guardians give the Orb to the Nova Corps for safekeeping. Drax the Destroyer, who got revenge on Ronan for killing his family, decides to turn his attention to Thanos, as the latter was the one who sent Ronan to kill Drax's family.

However, Thanos is still determined to find the six Infinity Stones and the Infinity Gauntlet so he can use them to conquer and rebalance the universe and this event would finally make him decide to come out to the open.

Avengers: Age of Ultron
Thanos is indirectly mentioned numerous times in this film; the first time was when Tony said of a possibility that a powerful villain would destroy the Avengers, which made Thor finally realize that someone has been manipulating the events (including Loki) to find the Infinity Stones. This was foreshadowed when Tony and Banner found Loki's scepter and used it to bring life to a peacekeeping A.I. program, which later became known as the homicidal cyborg Ultron, much to both Tony and Banner's distraught.

Gaining sentience from the power of the Mind Stone after breaking the scepter and killing HYDRA leader Wolfgang von Strucker, Ultron decides to utilize the Mind Stone in his plot to destroy the Avengers and all of humanity with his own army of Ultron Sentinels. Tony also suffered a nightmare (thanks to the powers of Scarlet Witch) where he sees all the Avengers being murdered (presumably by Thanos) while more Leviathans are heading towards Earth, foreshadowing Thanos' plot to take over the universe with the Infinity Stones.

Eventually, as Ultron and his Sentinels end up being destroyed by the Avengers at Sokovia while the Mind Stone ends up in the possession of Vision, Thanos finally appeared in a mid-credits scene, where he is fed up with losing his resources and his henchmen failing him and betraying him in his failed attempts to acquire the Stones. He goes into a white room in an unknown location and takes the Infinity Gauntlet from its hiding place, swearing to collect all of the six Infinity Stones (including the Mind Stone) by himself.

Guardians of the Galaxy Vol. 2
Thanos doesn't appear in the film, but is mentioned twice, once by Nebula (who angrily blames Gamora for the lifetime of pain and misery that she suffered at the hands of Thanos), and another by one of the Ravagers (led by Taserface) as he is aware that Nebula is Thanos' adoptive daughter. Eventually, after having a change of heart and helping the Guardians defeat Ego and the Sovereign, Nebula reconciles with Gamora but leaves her as she intends to kill Thanos and prevent anyone else from falling under his control.

Thor: Ragnarok
Thanos doesn't appear nor is mentioned in the film. However, his giant ship, the Sanctuary II is seen during a mid-credits scene as it was intercepting one of the Grandmaster's giant ships containing the Asgardians survivors following the deaths of Hela and the Berserker Army, as well as the destruction of Asgard, by the hands of Surtur. It can be implied that Thanos and his forces are going after the Space Stone (the Tesseract) that Loki saved from Ragnarok following Surtur's death.

Avengers: Infinity War
In the film, Thanos is first seen sending his elite team of adopted children (known as the Black Order) to attack the Asgardians' ship, being aware that Loki took hold of the Tesseract before Asgard's destruction. Thanos and the Black Order massacre all of the Asgardians and he personally beats Thor up with ease. Thanos is surprised by Hulk but he easily defeats him. As all of the Asgardians are being slaughtered while the Hulk is sent back to Earth to warn of Thanos' arrival, Thanos coerces Loki into surrendering the Tesseract by threatening to kill a beaten Thor. Loki does so but intends to reclaim it back for Thor by feigning loyalty to Thanos in an attempt to stab him with a dagger. Unfortunately, Thanos easily anticipates this move and lifts Loki while choking him. Thanos calmly mocks Loki for saying undying fidelity and is unfazed when Loki says he will never be a god, snapping his neck in front of a horrified Thor. It was later revealed that Thanos has previously acquired the Orb after invading and destroying the planet Xandar, and he uses the Orb to destroy the Asgardians' ship, leaving a helpless Thor to drift in space.

With two of the Infinity Stones in his possession, Thanos sent the Black Order to Earth to collect the Time Stone (the Eye of Agamotto) and the Mind Stone while he travels to Knowhere, where he most likely kills the Collector to get hold of the Reality Stone (the Aether). Using the Aether, which he turned back into the Reality Stone. Thanos conjured an illusion that succeeded to lure the Guardians into a trap. He proceeds to easily capture Gamora and calmly uses the Reality Stone to turn Drax and Mantis into pieces. Thanos then forces her into giving out the location of the Soul Stone by threatening to torture and kill a captive Nebula. Having no choice, Gamora confesses that the Soul Stone is in the planet Vormir and is guarded by the Stonekeeper (known as Red Skull). Traveling to Vormir with a captive Gamora, Thanos is told by Red Skull that he will give the Soul Stone, but only if Thanos is willing to sacrifice a loved one. Gamora laughs at this before claiming that Thanos doesn't care for anyone, but Thanos turns to her revealing tears, as she is the only thing and the only adopted children he truly loved; even the Red Skull points out that the tears are for Gamora. Despite realizing this, Gamora tries to commit suicide to ensure that Thanos cannot get the Soul Stone, but Thanos foils this and reluctantly kills her by throwing her off a cliff to gain hold of the Soul Stone.

With four Infinity Stones in place, Thanos travels back to his homeworld Titan, where he intends to wait for Ebony Maw to deliver the Eye of Agamotto. However, he found Doctor Strange waiting for him and instantly deduced that Maw is dead due to Tony Stark (Iron Man) killing him to save Strange (the current holder of the Eye). Unfazed, Thanos muses on his goals and then begins a ferocious battle with the majority of the Guardians, who have arrived after being contacted by Nebula, Iron Man, Spider-Man and Doctor Strange. Despite being outnumbered, Thanos proves to be too powerful to defeat easily and fights them off using the Gauntlet and his fighting skill and physical power effectively. However, Nebula arrives and although Thanos subdued her swiftly, the heroes barely managed to briefly subdue Thanos thanks to Nebula's distraction of Thanos. Despite this, Thanos still put up a fierce fight and eventually they learned that he has killed Gamora to get the Soul Stone, which provoked an angry Peter Quill to attack Thanos. Unfortunately, this breaks the heroes' group on Thanos, who then initiates the Guardians, forcing Spider-Man to save them from the oncoming meteor shower and making him unable to help Iron Man and Doctor Strange, before overpowering Strange's Magic and severely injuring Iron Man, although Strange surrendered the Time Stone to him so he would spare Tony, a deal that Thanos agreed to.

Meanwhile, Corvus Glaive, Proxima Midnight and Cull Obsidian assemble a massive army of Outriders to attack Wakanda, being aware that the hero Vision has the Mind Stone lodged in his forehead and is currently located in Wakanda. This forces several Avengers and the Wakandan warriors to fight back against Thanos's army. At first, the heroes are being overwhelmed, but Thor, Rocket Raccoon and Groot arrived at the rescue with a new powerful weapon called Stormbreaker, allowing the Avengers and Wakandan warriors to finish off Glaive, Proxima, Obsidian and the Outriders to their defeat and deaths. However, Thanos personally arrived on Wakanda after acquiring the Time Stone and managed to easily defeat the Avengers and Guardians, only to witness Scarlet Witch removing the Mind Stone from Vision and destroying it with her powers. Unperturbed by this, Thanos used the Eye of Agamotto to reverse this event, allowing himself to collect the Mind Stone while killing Vision at the same time, much to Scarlet Witch's distraught.

In a last-minute attempt to finish off Thanos, Thor imbued all of his power, further fueled by his strong desire to avenge Loki and the Asgardians and stop Thanos from achieving his goal, into Stormbreaker and managed to violently strike Thanos in the chest before using all of his strength to twist the axe as deep as he could into Thanos. Despite being severely wounded by Stormbreaker, Thanos has already infused all the Stones into the Gauntlet and sends out a death wave with a snap of his fingers in retaliation, taunting Thor that he should've aimed for the head instead. As a result, half of the universe's populace starts to disintegrate away to their demises (including several Wakandan warriors, Avengers and Guardians) while Thanos briefly enters into limbo, where he talks to a young Gamora about his successful goal, but not before tearfully admitting to her that it cost him everything he held dear. As a victorious Thanos escapes away, the surviving heroes are left horrified that they lost and that the entire universe is now in disarray due to losing their families, friends and allies to Thanos' death wave. A fully recovered Thanos is last seen watching a sunrise from another planet with a smile on his face, satisfied that he finally defeated the heroes and achieved his goal.