Thor's half-brother. He is the Norse god of Mischief.
Loki in comic continuity is the son of the Frost Giant King Laufey. When Laufey is killed in battle by Odin he is taken in by the All-Father as his adopted son. Odin raised him alongside his other son, the Thunder God Thor.
Loki's mischievous and plotting ways normally lead to trouble between him and the rest of Asgard. Loki wants nothing more than to rule Asgard. He also often plays a key role in the formation of the Avengers, almost always inadvertently.
In 965 AD, the Frost Giants of Jotunheim attempted to conquer all nine realms. However, they were defeated by Odin (Antony Hopkins), the king of Asgard, and his troops. As a prize for their victory, Odin took the Casket of Ancient Winters, an object that contains the source of Frost Giant's power.
In the present day, Thor (Chris Hemsworth), son of Odin is about to inherit his father’s throne, but the ceremony is interrupted when Frost Giants invade to take back the Casket of Ancient Winters. This invasion is put down when Odin summons the destroyer, who obliterates the thieves. After the battle, Thor suggests that Odin makes war with the Frost Giants for their intrusion. Odin, in all his wisdom, refuses to act on Thor's suggestion on the grounds that the thieves have already been punished and he would not want to shatter the truce between the two kingdoms.
Noticing Thor’s frustration, Loki (Tom Hiddleston), his brother,agrees that Thor’s suggestion was the right idea. Emboldened by his brother’s assurance, Thor decides to invade Jotunheim with the Warriors Three, his childhood friend Sif (Jamie Alexander), and Loki. The company tries to enter Jotunheim by the way of the Bifrost, Asgard’s gateway, but they are confronted by Heimdall (Idris Elba), the guardian of the gate, who blocks their path. Loki tries to persuade Heimdall to let them but it leads to no avail. The Thor tries to persuade Heimdall and they are allowed to pass through. Heimdall warns that if they bring back an invasion force, he seal the gate to Asgard whether they return or not.
At Jotunheim, Thor speaks with the king of the Frost Giants,Laufey (Colm Feore); he asks why there were Frost Giants in Asgard. Laufey responds by saying there are many traitors in Asgard and that he had nothing to do with the attack. Thor is unsatisfied with the answer and is provoked by who Laufey, who questions his manhood. At the same time, Frost Giants surround the area. Thor, who is insulted by Laufey’s remark, begins attacking the Frost Giants. An epic battle ensues, but Thor and his companies are eventually overwhelmed by the sheer number of Frost Giants. It is then that Odin swoops in and saves Thor and his company, but it is at the cost of the truce. Outraged by Thor’s disobedience, Odin strips Thor of his powers and send him to Earth. He also sends Mjolnir, Thor’s hammer, to Earth and declares that if a worthy person picks up the hammer, they shall receive all the powers of Thor.
Later, Sif asks Loki to try to change Odin’s mind of the matter of Thor. Loki, who had always been jealous of Thor, declines because he has nothing to gain from Thor’s return and says that with Thor as the king, his rule would only bring more problems to the kingdom. Loki leaves the room and enters the relic room. There, he touches the Casket of Ancient Winters and begins transforming into a Frost Giant. At that moment, Odin enters the room and asks what Loki is doing. Furious, Loki begins shouting at his father and demands to know the truth about his life. Odin reveals that when he had defeated Laufey at Jotunheim, he had not only taken the Casket, but also Loki, the son of Laufey, as his own adopted son. This revelation only angers Loki and he accuses his father of favoring Thor over him. Odin responds by saying that he had hoped that he would use Loki to forge a more permanent alliance between Asgard and the Frost Giants. Loki responds by fuming at his adopted father. Odin who is stressed by the matters has a heart attack and falls to the ground. The guards rush in and take Odin into another room and Odin enters into a deep sleep, known as the Odin-sleep, to recover his strength.
With Odin incapacitated, Loki becomes the regent of Asgard. Since the power has changed hands, Sif asks Loki to pardon Thor and release him from his banishment. Loki declines because he cannot overrule an order given by Odin. Then Volstagg (Ray Stevenson), one of the Warriors Three, asks Loki once again to reconsider his decision. At this Loki is furious and he demands that Sif and the Warriors Three leave the room. Upon hearing that Thor has been captured by mortals, Loki visits Thor and informs him that Odin has died and that he is the new regent. Thor asks if he could return to Asgard, but Loki says his mother prohibits Thor's return. Before leaving Loki attempts to pick up Thor's hammer, but he is unable.
Next, Loki travels to Jotunheim, in order to make a deal with Laufey. Loki reveals that he is the one who allowed the Frost Giants into Asgard and that he could allow Laufey entrance into Asgard so he could kill Odin. Laufey asks why Loki did not simply kill Odin with his own hand, and Loki responds by saying that the people of Asgard will look negatively upon him if their new king ascended to the throne by spilling the blood of the former king.
Meanwhile, Sif and the Warriors Three decide to go to Earth to search for Thor. They are granted passage by Heimdall, but their passage is still discovered by Loki, who sends the Destroyer to finish them off along with Thor. Then Loki allows Laufey to enter the realm with two of his Frost Giants. In a surprising turn of events, Loki betrays Laufey and kills him. It is at this moment that Thor, having recovered his powers and knowing that Loki attempted to kill him, arrives with his friends. Loki attacks Thor and heads towards the Bifrost. Loki opens the portal to Jotunheim and uses the Bifrost Bridge to destroy Jotunheim. Thor confronts Loki and asks why he had changed so quickly. Loki responds that he wanted Odin to think he was worthy and he couldn't stand the decisions that Thor was making. Thor is angry with Loki's arrogance and uses Mjolnir to smash the bridge. This prevents the planet of Jotunheim from being destroyed, but it also prevents Thor from returning to Earth. The resulting explosion from the bridge causes Loki to fall into a black hole.
In a post credits scene, Dr. Selvig (Stellan Skarsgård) meets Nick Fury (Samuel L. Jackson) in an underground facility. They discuss the legend, history and the possibilities that Thor's arrival has opened up for mankind. Nick Fury shows Dr. Selvig a case that contains the cosmic cube, a source of perhaps unlimited power. Loki appears in the mirror and says "Well, I guess that's worth a look." Dr. Selvig repeats Loki's lines and it is implied that Dr. Selvig is under Loki's control.
Loki is also an antagonist on the Avengers: Earth's Mightiest Heroes television show. Show-runner Joshua Fine once stated that Loki is his favorite villain on the series and one of three primary antagonists for the team, along with Kang the Conqueror and Ultron. In the show, Loki similarly attempted to usurp his father's power on Asgard, while also manipulating events on Earth to keep Thor busy. His plans were eventually defeated by the newly formed Avengers and he was exiled to the clutches of the World Serpent, a giant Asgardian monster, at the end of Season 1.
Loki is the God of Lies and Mischief. He is constantly scheming trying to manipulate the people around him for either his own gain or his own amusement. Loki's schemes are often multifaceted and complex, and hardly any action isn't extremely crafted and planned. He should never be trusted, no matter how well-meaning he may appear.
Loki feels a since of entitlement to the throne of Asgard, feeling he would make a far better king than his more brave but less crafty adoptive brother Thor. He also resents Odin for lying to him about his parentage for most of his life. He occasionally shows allegiances to the Frost Giants, sworn enemies of the Asgardians, but this is often merely to advance his own schemes; the only person Loki is truly loyal to is himself.
Being a child of a Frost Giant, Loki is resistant to the cold and has the power to use ice magic. As a god, Loki can endure greater damage, live for hundreds of years and teleport without the use the bifrost. His notable are his magical skills. Loki is able to create illusion, create copies of himself and conceal himself and those around him from sight. He can also summon objects out of thin air, like he did when he summoned the Casket of Ancient Winters. In addition, Loki can control or influence other being such as human with his mind.