Chitauri

The Chitauri are an evil extraterrestial race of shape-shifting humanoids and villains in Marvel comics. They served as the secondary antagonists in the 2012 movie The Avengers and they are Loki's personal army, and posthumous antagonists in the later parts of the Marvel Cinematic Universe.

History
The race called Chitauri appeared as Ultimate Marvel's (Earth-1610's) counterpart to the Skrulls. They are a shapeshifting alien species who have attempted to conquer the Earth, most notably during World War II and again in the early 21st century.

The Chitauri claim to be part of "the immune system of the Universe", wiping out disorder and free will wherever they find it. They seem to prefer to act behind the scenes, mimicking and influencing the social and military methods of the species they are currently infiltrating. For example, they aided the Nazis in their attempt at world conquest by providing them with the technology to create a nuclear bomb carried by an intercontinental ballistic missile. However, this attempt was thwarted by the prototype super-soldier codenamed Captain America. Through the entire conflict of World War II, the Chitauri were being driven out of their operations in Africa and Europe, even from their main Japanese training camps in Hiroshima and Nagasaki. Following the end of the war, the Chitauri withdrew to make new plans.

The next attempt at conquest was more subtle (at first), involving long-term methods of manipulation such as will-inhibiting drugs in many nations' water supplies, influencing the media, and R.F.I.D. (radio-frequency identification) microchips to be implanted in schoolchildren, among other means. The Chitauri also infiltrated S.H.I.E.L.D., particularly the Psi-Division which could telepathically ferret out Chitauri agents. However, S.H.I.E.L.D. was able to detect some of the low-ranking "drone" staff of the aliens, disguised as common office workers, and wiped them out in an assault led by Black Widow and Hawkeye.

The Chitauri planted false information through the compromised Psi-Division that led S.H.I.E.L.D. and the Ultimates into a trap on a small Micronesian island; due to the combined efforts of Iron Man and Thor, the Ultimates, Nick Fury and a handful of SHIELD soldiers survived, but thousands of S.H.I.E.L.D. soldiers were killed and dozens of Helicarriers were destroyed.

The Chitauri then counterattacked by infiltrating the Triskelion and capturing The Wasp. The Chitauri leader, known only by his former Nazi identity as Herr Kleiser, took the Wasp to a hidden Chitauri base in Arizona. However, their location was given away when a fleet of damaged Chitauri starships suddenly entered Earth's atmosphere to hover above the formerly secret base, claiming that they were fleeing major defeats across the galaxy by their intergalactic enemies and that the remainder of their forces are forced to the "backwaters" of the Milky Way Galaxy (i.e. Earth's solar system). Disregarding Herr Kleiser's long efforts, the Chitauri ordered him to destroy Earth and its solar system with a doomsday bomb as part of a scorched-earth policy and retreat to the "lower fourth-dimension". The Ultimates and all available S.H.I.E.L.D. and military forces immediately converged on the alien fleet.

Although Iron Man and Thor were able to damage the ships (who as well in ridding the Chitauri bomb by teleporting it to the wastes of Nastrond, where its detonation caused only a small ripple in space-time), it was the Hulk who downed the majority of the fleet. At the same time, Captain America battled his old enemy Kleiser, but was unable to defeat him alone. At Captain America's urging/mocking of Kleiser touching Betty Ross (Hulk's crush), the Hulk was able to beat, dismember, and devour Kleiser. It is presently presumed that the combination of the Chitauri's series of intergalactic defeats and the destruction of the Chitauri fleet on Earth spelled the complete and total defeat of the alien race.

Powers and Abilities
The Chitauri were able to mimic human form and absorb human knowledge, apparently by ingesting the bodies or brains of the humans they imitated. In their natural form, they appear to be large, and reptilian, but no clear images of their native form have been shown. Although the drone workers were nearly mindless and not much more durable than ordinary humans, the high-ranking officers such as Kleiser possessed enough strength to rival Captain America, superhuman stamina and durability, extremely rapid regeneration, and the ability to see or sense invisible objects or people. The Hulk proves to be strong enough to destroy and consume Kleiser.

Comparison with Skrulls
Another race called Skrulls, physically resembling the Skrulls of the mainstream Marvel universe appear later (led by the billion-year-old Skrull Emperor, Kl'rt); these Skrulls dislike being confused with the Chitauri, whom they call terrorists. They have extremely advanced technology, but have not been observed to shapeshift. These Skrulls were seen only in an alternate timeline in which Reed Richards contacted their world via his teleporter. The events leading to that timeline were altered in Ultimate Fantastic Four #29 and contact was never made.

Ultimate Avengers and Ultimate Avengers 2
The Chitauri appear in the 2006 animated movies Ultimate Avengers and Ultimate Avengers 2 as the main antagonists and the enemies of the Avengers and S.H.I.E.L.D. Unlike their appearance in The Ultimates, they do show their true form: seven feet tall reptilian creatures with dark greenish skin, and fire blasts from their hands.

The Avengers
In the 2012 film The Avengers, the Chitauri are a race of grey-skinned, six-fingered reptilian humanoids that have a heavily cybernetic or biomechanical physiology. They are the tertiary antagonists of the movie. These Chitauri display none of their shapeshifting capacities from the Ultimate universe, but have highly advanced technology, such as hovercraft-like skimmers, staves that also operate as rifles and large airborne troop carriers (known as Leviathans) that resemble biomechanical arthropods or limbless reptiles, encased in mechanized armor. They seem to have a neural link to their mothership as, when Tony Stark/Iron Man destroys the ship with a hijacked nuclear missile, the aliens seem to drop dead instantly.

They are thought to be led by one hooded Chitauri creature called "The Other" (played by Alexis Denisof). During the conversations had between the Other and Loki, the Other repeatedly mentions a powerful being later revealed in a mid-credits scene to be Thanos.

After The Avengers
The Chitauri remained posthumous antagonists in later films.
 * In Iron Man 3, Tony Stark gets repeated panic attacks from flashbacks of himself leading the nuke into space and straight at the Chitauri mothership.
 * In Thor: The Dark World, Loki was imprisoned by Odin to pay for his crimes on Earth. This in turn leads to him faking his death, sneaking back to Asgard, killing Odin and taking his place as king of Asgard. It couldn't have happened if the Chitauri invasion didn't leave Loki in prison in the first place.
 * In Captain America: The Winter Soldier, HYDRA used the Chitauri invasion as an excuse to build anti-alien Helicarriers, as well as using terrorist-hunting as another excuse. However, these were actually built to destroy any and all future threats to HYDRA. This leads to S.H.I.E.L.D. being disbanded and rebuilt, due to HYDRA being inside S.H.I.E.L.D. for decades. In the mid-credits scene, we see that a HYDRA agent named Wolfgang von Strucker is collecting things of power; two prisoners are shown, Quicksilver and Scarlet Witch, while one of these items shown is Loki's mind-control staff, which was a Chitauri weapon.
 * A strong level of the Chitauri's legacy is presented several times in the TV series Marvel's Agents of S.H.I.E.L.D. When Coulson was brought back to life using the blood of a Kree alien, a hacker group called the Rising Tide set in and proclaimed that the secrets are out, aliens are real and S.H.I.E.L.D. has been lying to the world about many things. In the pilot episode, a S.H.I.E.L.D. agent/HYDRA double-agent named Grant Ward goes to an arms-dealer's home in Paris and manages to steal a "Chitauri neural link". What it does is unknown, but it might have been why they all died when the mothership was nuked in The Avengers. In the episode "F.Z.Z.T", several firefighters were sent to New York after the invasion, with one fireman from a small Pennsylvanian town taking a Chitauri helmet home as a souvenir. However, it housed an alien virus that spreads by static shock and slowly killed the firefighters who caught the shock; an explsoion of light would occur, and the body would be floating in mid-air. In the episode "The Magical Place", it is implied that salvaged Chitauri metal was used in the technology for the Centipede Serum seen several times throughout the series.
 * The Other makes another appearance in Guardians of the Galaxy, but Ronan the Accuser breaks his neck. A Chitauri prisoner was shown later in the movie among the collected items of Taneleer Tivan's museum.

Trivia

 * In The Avengers, The Chitauri play a similar role to the army of Parasimon in the Digimon Tamers movie Runaway Locomon; Both are an invading army who are able to enter Earth through some sort of portal activated by an ally (or pawn, in the case of Parasimon), both serve the purpose of having all the heroes fighting alongside each other against an army of enemies individually weak enough for them to destroy, and both are ultimately destroyed when the main character sends an attack through the portal. Although while the Parasimon leader is killed along with his army, The Other survives.
 * Their role in The Avengers has led to many events happening in the Marvel Cinematic Universe; without the Chitauri invasion, many major events in the franchise wouldn't have been.