Loki is the main antagonist of Thor and The Avengers, the tritagonist/anti-hero of Thor: The Dark World, the deuteragonist of Thor: Ragnarok, a supporting character in Avengers: Infinity War and a posthumous character in it's untitled sequel.
Loki initially appeared as a supporting character in Thor, but gradually became the true main antagonist after he was revealed to be the biological son of Laufey.
Admittedly jealous of his adoptive brother Thor and anxious about a kingdom ruled by the loud and violent God of Thunder, Loki allowed several Jotuns to enter Asgard during Thor's coronation (Loki later admitted that it was "just a bit of fun" meant to ruin his brother's special day and to keep Asgard from his reign for a short while longer). In the wake of this intrusion, Thor was eager to launch a counterattack and Loki appeared to attempt to dissuade him while possibly actually goading him into action. On leaving, Loki left word with a guard to inform Odin of their departure, although whether this was out of concern for their safety or desire to make Thor lose favor with Odin is unclear.
Once in Jotunheim, Thor led himself, Loki, Sif and the Warriors Three into conflict and attacked the Jotuns even after being granted safe passage home by Laufey. During the ensuing fight, Loki used 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 was then attacked by another that seized him by the wrist. Loki was then surprised by his own resistance to the Jotuns' freezing touch and saw his flesh turn Jotun blue and then return to Asgardian color, a revelation that sowed doubt about his origins in his mind. Odin arrived and took the group back to Asgard after Laufey promised that Thor would have the war and death he desired. After arriving back in Asgard, Thor and Odin exchanged heated words and insults until Odin, saddened by his son's arrogance and lack of wisdom, decided to punish him. Loki tried to intercede on his brother's behalf but was given a stern reprimand by Odin, prompting him to withdraw and be silent. Odin banished Thor to Midgard (Earth) while Loki watched in horror; Odin also sent Mjolnir, enchanting it to only allow a worthy person to lift it and acquire the Power of Thor.
Loki, Sif and the Warriors Three went to the healing room to treat their wounds. Still wondering about the changing of his flesh on Jotunheim, Loki decided to see if he could induce it using the Casket of Ancient Winters. While he lifted it, his skin up to his hairline turned Jotun blue and his eyes turned Jotun red. He was then interrupted by Odin and confronted him regarding the incident. Loki learned that Odin discovered him as an infant left to die in the Jotuns' temple during the final battle of the ancient war. On Loki's heated insistence, Odin also revealed 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 stated that those plans no longer mattered. Infuriated that he had been lied to and had been taunted with the promise of a possible birthright, Loki shouted hatefully at Odin and, overwhelmed by the stress of his family falling apart coupled with the impending war with Jotunheim, Odin fell into the Odinsleep in front of him.
With Thor already banished to Earth for the attack on Jotunheim, Loki was offered the position of King by Frigga and assumed the role of Asgard's regent. From his position of power, he went briefly to Midgard to lie to Thor (who had been captured by S.H.I.E.L.D.), telling him their father had died and that their mother forbade his return, as well as trying unsuccessfully to take Mjolnir for himself. Loki then visited Jotunheim under the guise of trying to repair the damage his brother had done, but instead offered Laufey a chance to slay Odin while he slept, promising to return the Casket to him in return, which Laufey accepted.
When Sif and the Warriors Three disobeyed Loki's command to wait for his word by going to Midgard to retrieve Thor, Loki confronted and froze Heimdall for allowing them to leave. He then sent the Destroyer after them to eliminate everything in its path and ensure that Thor could not return home. This action proved his undoing when Thor's courage in confronting the automaton paved the way for his return, and just as Loki betrayed and killed Laufey in Odin's chamber, Thor arrived to challenge him over his actions. The resulting fight quickly moved to Heimdall's Observatory where Loki had connected the Bifrost to Jotunheim, threatening to destroy it. Thor's power ultimately overpowered Loki's cunning, at the cost of the observatory and the Bifrost.
As Loki fell into the abyss below, the spear in his hand was grabbed by Thor who, in turn, was anchored to the remnants of the bridge by the newly-awakened Odin. Loki appealed to his adoptive father that, by annihilating the Jotuns, he was doing what was best for Asgard. Odin sadly rejected this and, with his Asgardian life now in tatters, Loki released the spear and allowed 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 S.H.I.E.L.D. to turn his scientific knowledge to the task of unlocking the secrets of a mysterious blue-glowing cube, which would supposedly be the key to unlimited sustainable energy for Earth. Loki's apparition whispered words of encouragement to proceed.
Loki returned 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. He made his first appearance in the film when he emerged from the portal created by the Tesseract at the S.H.I.E.L.D. building. He brainwashed Clint Barton/Hawkeye, Selvig and various other S.H.I.E.L.D. agents, and took the Tesseract. The portal created by the Tesseract resulted in the destruction of the building, though S.H.I.E.L.D. director Nick Fury survived, as did Agents Phil Coulson and Maria Hill. Fury decided that Earth was in danger and decided to assemble the Avengers.
After securing an area to determine the next course of action for the cube, Loki noted the scepter's gem glowing and calling out to him. He then allowed himself to enter a trance where he could appear to the Other, the Chitauri's leader, and his army in a metaphysical form. The Other warned Loki that if he failed in his pursuit of Earth and the Tesseract didn't fall into their hands to be given to Thanos, there would be no place for him to hide from the overlord's wrath and that he would beg for something as sweet as pain. Now unsettled about potential failure and more determined than ever, Loki went to Stuttgart, Germany with Hawkeye and other turned agents in order to retrieve iridium needed to stabilize the portal. He disrupted a gala at a large museum while Hawkeye raided a secure installation for iridium. Loki struck terror into the hearts of patrons and guests by securing the one thing needed for Hawkeye to breach the iridium lock's security measures: the curator's eyeball.
Loki then strode out after the screaming crowd into the streets where he made several copies of himself, trapping the people, and demanded that they kneel before him. He then bragged that this was man's purpose, but a single man challenged him and his intentions. When Loki prepared to kill the old man, Captain America appeared and challenged him. Seconds later, the Quinjet, piloted by Black Widow, also challenged him from the sky. After a brief battle with the super-soldier, during which Loki had the upper hand, Iron Man arrived and threatened to fire upon Loki, daring him to make a move. Outnumbered, Loki allowed himself to be captured, secretly plotting to use this to his advantage. As they journeyed to the S.H.I.E.L.D. Helicarrier, Thor arrived and extracted Loki from the jet.
Back on the ground, Thor attempted 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 resented his brother and refused to cooperate. Thor was then tackled by Iron Man before he could say any more, and Loki remained on his perch as he watched the two battle before agreeing to ally themselves with Captain America. They took him into S.H.I.E.L.D. custody aboard the Helicarrier, where he was placed in a confinement capsule designed to hold the Hulk. Loki taunted Fury about his attempts to control the Tesseract and his gathering of misfits to defend Earth.
Loki's mere presence was enough to provide a disruptive element that would fragment 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 Hawkeye's freedom, Loki subjected her to a play of wits where he ferreted out her deeper misgivings, but was completely caught off-guard when she tricked him into revealing that there was already a monster among them and that it was not him. From this, she concluded that the monster in question was Bruce Banner and that Loki was planning to use the Hulk to destroy the ship and the heroes as well.
However, Loki's plan to use the Hulk, only one aspect of his real intentions, did follow through as another jet carrying Hawkeye and the rogue agents came to his aide, 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 used an illusion of himself to trick Thor into entering the cell and to distract Coulson. Loki mortally wounded Coulson and ejected Thor's cell from the Helicarrier. Though Loki retrieved his scepter, Hawkeye was released from his mind control, and Loki headed to New York, where Selvig waited with the Tesseract at Stark Tower.
Loki prepared to welcome his army and begin his glorious, but brief, war on the earth. Tony Stark, still alive after the raid and having figured out his plan, caught up with him at the Tower and abandoned his wrecked Iron Man suit to threaten him. When Loki grew weary of the threats, he tried to subjugate Stark with the scepter, only to be physically blocked by the arc reactor in Stark's chest. Annoyed, he threw the inventor out of a window, and was surprised when a freshly-built Iron Man armor rocketed out after the man. Loki found himself briefly under attack when the fully suited Iron Man rocketed back up to retaliate before the Tesseract opened the portal, allowing the Chitauri to come pouring through. With his triumph near at hand, he was confronted by Thor, who demanded that he at once deactivate the Tesseract or the thunder god would destroy it. Loki refused, claiming that nothing could stop his war.
The brothers fought a second time, Loki's scepter matching Thor's hammer. Blasts from the gem almost completely destroyed the Stark Tower logo on the side of the balcony, blasting the giant letters and debris off the side. When the confrontation came to stalemate with them grappling each others' necks, Thor urged Loki to look around him at the destruction he caused and asked if he truly believed it would all end with his rule. While Loki was unsure of himself, his eyes reverted to their normal green state temporarily as he claimed it was too late to stop the madness, but briefly considered Thor's appeal to work together to end it all and redeem himself. The will of the Tesseract over his mind was stronger than his guilt, however, and he instead stabbed Thor with a throwing knife, preparing to strike him down with the scepter as he knelt before him and laughing in amusement at the sentiment. This did little more than enrage the thunder god, who disarmed his adoptive brother of his staff and picked him up before slamming him down hard on the ruined balcony.
Loki threw himself off the building as he was defeated and managed to land on one of the Chitauri's small flying craft. From there, he led an attack on the city. When the first of the Chitauri's massive Leviathans was destroyed by the Hulk, he commanded the Chitauri on the other side of the still-open portal to send the rest of their massive armada, overwhelming the city's defenses. An aerial chase after Black Widow left his craft destroyed by one of Hawkeye's arrows and Loki landed back on Stark Tower, where the Hulk confronted him. Loki's frustrated rant goaded the Hulk into simply picking him up and repeatedly slamming him into the ground. Loki was 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 six of the Earth's mightiest, having defeated the Chitauri army and closing the portal, taking it in pretty good stride, however, he simply calmly requested the drink that Stark had offered before. After the Tesseract was relinquished to Thor, Loki was bound and placed in a metal muzzle (likely to prevent pleading, threatening or perhaps using magic) and led to an open area in Central Park with his brother. From there, Thor used the power of the Tesseract to transport both of them home to Asgard.
Thor: The Dark WorldEdit
Loki returned as the tritagonist/anti-hero. After being returned to Asgard, Loki was brought before Odin and Frigga in chains. The Tesseract still messing with his head, Loki was unable to understand what he had done wrong and argued with Odin, explaining to the Allfather that he had attempted to rule Earth as a god like Odin and displayed a desire to be executed in favor of speaking with him any longer. Due to Frigga still loving him, however, Loki was sentenced to life in prison.
Presumably two years later, Loki is next seen chatting with Frigga, who had visited him in his cell as a hologram. Loki still felt his actions on Earth were justified, and he was secretly hurt that neither Thor nor Odin had come to visit him. All Loki had to keep himself entertained were books that Frigga had given him, which he was later seen reading due to a lack of anything else to do. Loki's was the only cell that Kurse did not break open during his rampage though, with a lingering desire for Asgard to fall, Loki gave Kurse directions to the palace's shield generator. Following said directions, Kurse destroyed the generator and killed Frigga. Loki was not invited to her funeral, but when informed of her death, the Tesseract's hold on him, along with his heart, broke and Loki destroyed the inside of his cell in a burst of guilt and fury.
When Thor came to Loki for help, the latter attempted to magically conceal the true appearance of himself and his cell, but was unable to do so for long. After letting the spell wear off, it was revealed that Loki had let himself go, his feet cut and bleeding, and his hair long and greasy. Thor offered Loki a chance to avenge Frigga, which he happily accepted. Now out of his cell and free to thrive, Loki seriously annoyed Thor with his magic. He turned himself into an Asgardian soldier, Thor into Lady Sif and then himself into Captain America, prompting Thor to cuff him. After being threatened by Sif, Thor, Volstagg and slapped by Jane, Loki constantly pestered Thor during their escape to Svartalfheim. Whilst searching for the Dark Elves, Loki and Thor got into a heated argument which almost resulted in a physical fight but their mutual love for Frigga calmed them down. Upon locating Malekith and his henchmen, Loki persuaded Thor to uncuff him. He then instantly stabbed Thor in the stomach with a dagger, kicked him in the head and cut off his hand, declaring he never loved Frigga and only ever desired to kill Thor and Odin. Throwing Jane to Malekith's mercy, Loki expressed an alliance with the Dark Elves if it meant he could watch Asgard get destroyed. Accepting this union, Malekith drew the Aether out of Jane but before he could absorb it, Loki revealed he and Thor had tricked the evil elf. Loki revealed Thor's injuries, including the loss of his hand, to be an illusion. He then dived on top of Jane to shield her as Thor's lighting strike at the Aether caused a large explosion. The action was a failure,
however, as the Aether survived the assault and Malekith successfully absorbed it. A Dark Elf then threw a vortex grenade at Jane, but Loki grabbed and threw her out of the way, taking the blast himself. He almost died as a result, but Thor saved him. While Thor fought Kurse, Loki was surrounded by the remaining Dark Elf foot soldiers. He singlehandedly killed them all, however, and saved Thor from being pummeled to a pulp by Kurse by stabbing the monster with a spear. Kurse, unharmed, impailed Loki with the same spear and threw him to the ground, but Loki had set off Kurse's grenades, destroying him and avenging Frigga. Thor cradled his brother in his arms and the two made peace before Loki passed away, leaving Thor grief-stricken and Jane feeling sympathetic. However, Loki survived and made his way to Odin, disguised as a warrior and telling him Loki's body was found. Later, he was disguised as Odin, taking his place on the thrown unbeknownst to Thor or possibly anyone else, leaving questions open for Loki's future actions.