In Asgard, Loki escapes from the tree which entrapped him for ages and comes to Earth to get revenge on Thor. He hypnotizes his foster brother to separate him from his hammer, but a minute later, Thor's transformation into Don Blake puts an end to his hypnotic control. Thor defeats Loki and uses his hammer to send him back to Asgard.
Condemned by Odin to remain in Asgard forever, Loki leans through magic the connection between Dr. Drake, Thor and his hammer. He goes to Dr. Blake's office and informs Thor that he knows about his secret identity. Loki manages to separate him from his hammer hoping to turn him forever into his human form. But Thor outsmarts him and brings him back to Asgard again.
While he is confined in Asgard, Loki finds a mind reader who would turn evil if given more power so he decides to increase his ability to a level where he could even defeat Thor. His dreams are crushed when Sandu tries to lift Thor's hammer with his mind and the strain causes him to lose his powers.
Loki has been chained to a rock in Asgard as punishment for his last actions and vows revenge on Thor. Using his supernatural vision, he watches Thor playing in a film and when the Thunder God hurls his hammer at a mountain, he seizes the opportunity to make it fly to Asgard and break his Uru chains. Then he decides to make Thor come to Asgard where he has a better chance to defeat him. After learning that he is on the loose, Odin, Heimdall and Frigga find him and devise a better way to imprison him.
Chained in Asgard, Loki uses his magic so that Thor is hit by his hammer, which causes him to turn evil. Thor now willingly sets him free and they confront Odin to announce that they will terrorize Earth until he surrenders Asgard to them. Then they go on a rampage around the globe and the United Nations finally accept to appeal to Odin. But Odin and the Gods of Asgard reveal themselves in the assembly and cause Thor to be hit again by his hammer which restores his normal personality. Thor subdues Loki who is chained up in Asgard again.
Still chained in Asgard, Loki is visited by Thor who accuses him of altering the trajectory of a valuable missile. However Loki informs his foster brother that it is Merlin who is behind this and that he will find the culprit in Washington D.C.
Still held captive in Asgard, Loki remotely uses his magical powers to trick the Hulk into committing an incident that will force Thor to hunt him down. His plans are compromised when Iron Man, Ant-Man and the Wasp also show up to lend a hand. When he sees that Thor is coming to Asgard to visit him, he tries to stop him with all sorts of traps but the God of Thunder finds him anyway. He takes Loki back to Earth where he forces him to confess that he framed the Hulk for a train incident to set a trap for his foster brother. Then Loki gets trapped inside a lead-lined tank after unwillingly causing the creation of the Avengers.
From Asgard, Loki watches as Thor is denied by Odin the right to marry Jane Foster. He remembers that he brought the Lava Man to the surface as a prank and decides to pit him against his heartsick foster brother. But Thor manages to defeat the Lava Man and send him back to his underground world.
Young Thor takes his brother Loki to confront the Storm Giants to recover the Golden Apples that they stole from Iduna. After Loki has created a diversion, they locate the Apples with Agnar, the King of the Eagles that the Giants were holding prisoner. Then they free Agnar and fly away with the Golden Apples.
Odin agrees with Loki's plan to send the Enchantress to Earth to seduce his son but the Goddess fails.
Young Loki creates hole in Asgard's defenses and lets the evil forces know about it. Then he sends Thor alone to guard the breach in hopes that he would be destroyed. But the young god holds his own until Odin's army repels the intruders.
Loki tricks Dr. Strange into stealing Thor's hammer, but when the sorcerer realizes that the evil he felt came from the God of Mischief, they both engage in a mystical combat. Strange returns the hammer to his rightful owner and seeing that Thor is coming after him, Loki stops fighting and vanishes to Asgard.
As an infant, Loki was kept hidden by his father Laufey who was ashamed that he was not born a giant. After his father was killed in battle by Odin, the child was adopted by the ruler of Asgard and became Thor's foster brother.
Loki persuades Odin to cut Thor's power in half to punish him for still loving Jane. Then he restores Zarrko's memory of his defeat by Thor so that he'll seek revenge. Loki gloats at Odin's outrage when he sees that Thor has surrendered to Zarrko, but the Thunder God appears to regain Odin's favor when they see him defeat the Tomorrow Man.
The God of Mischief suggests that Odin travel to Earth to deal with Thor himself. Given the power to rule over Asgard in the monarch's absence, Loki releases Skagg the Storm Giant and Surtur from the prisons where Odin had entrapped them. The combined efforts of Odin, Thor and Balder are too much for the evil beings and they are defeated. Odin later condemns Loki to serve the Trolls for his betrayal.
Loki forces the Norn Queen to reveal Balder's only vulnerability, but having also sworn to protect the brave warrior's life, she ruins the God of Mischief's attempt to kill him.
Odin banishes the Enchantress and the Executioner to Earth for attacking his son, which pleases Loki who knows that they can still pose a threat to Thor there.
During Odin's absence, Loki escapes to Earth. Disguised as an old man, he enters Dr. Blake's office and separates him from his cane before running away with Jane Foster whom he sends to Limbo. Discovering that she is protected by a mystic force, Loki is forced to bring her back by his brother. He is taken back to Asgard by one of Odin's warriors.
Loki bails Mister Hyde and the Cobra out of jail and increases their strength so they can go and capture Jane Foster. He tricks Odin into banishing Thor, but the God of Thunder breaks into Asgard to confront Loki about Jane's abduction. Then Odin sends Loki on a quest to get a cure for the injured girl, but Balder is suspicious and takes over.
In the Forbidden Forest, Thor, Balder and Loki are challenged by Sigurd. Knowing about their opponent's power, Loki encourages his brother to fight him. But Balder tells Thor about the secret behind Sigurd's growing strength and Thor gets rid of the enemy by hurling him into space.
Delighted that Odin has removed Thor's powers because he gave up his birthright for Jane, Loki prevents other Asgardians from going to Earth to protect his foster brother. He is strongly disappointed when Odin finally changes his mind and restores his son's powers.
During a combat tournament, Loki cheats to get his favorite the advantage. When the attendees want to punish the culprit, Thor insists to share the reprimand, thus earning the respect of all warriors who spare them both. When Thor also wins a horse race, the jealous Loki vows that one day he will destroy his foster brother.
Unable to affect Thor's power with a potion, Loki decides to give superpowers to Crusher Creel a convicted brutal sociopath who becomes the Absorbing Man and breaks out of jail. While the villain is facing Thor in battle, Loki takes the opportunity to capture Jane Foster to lure his step-brother's to Asgard where he has more chances to match his powers. His fight against Thor is interrupted by Odin to whom he pretends that Thor has brought a mortal to Asgard. The All-Father decides to submit them both to the Trial of the Gods.
For the Trial of the Gods, Odin sends Thor and Loki to where they are to survive without any weapons. The first to come back shall be declared victorious. Loki informs Thor that he has sent the Executioner and the Enchantress on a visit to Jane Foster. And despite Odin's rules, Loki has brought enchanted Norn Stones with him and uses them to easily go past all of Skornheim's traps, enabling him to finish first. Thor is granted 24 hours by Odin to find proof of Loki's deceit. Visited by the Norn Queen who wants her stones back, Loki informs her that he still needs them to lure Thor into a trap. When his schemes to have the Viet Cong kill Dr. Blake fail, he takes control of a greedy hunter and leads him to the temple of the Destroyer. Realizing that the activated Destroyer may actually kill Thor instead of simply making him lose the stones, Loki, fearful of Odin's wrath, tries to inform the All-Father. Unfortunately for him, his father is sleeping the Sleep of Life and guards throw him into the Dungeon of No-Escape to prevent him from awakening their king. Within his cell, Loki manages to free Thor from the Destroyer's trap by making his ste-brother's body unsolid. Exhausted, Loki uses a last spell to contact the Norn Queen and gets her help to awaken and inform Odin. Knowing that Loki has caused the Destroyer to be activated, Odin binds his evil son in servitude to his royal Warlock Ularic.
Still serving Ularic, Loki gases his new master with a Suspended Animation Mist and hides him in the warlock's own Time Vault. Then he restores the Absorbing Man's molecular integrity and brings him back to Earth to face Thor again while he schemes to overthrow Odin himself. When Odin sends his warriors on patrols, Loki takes the opportunity to teleport the Absorbing Man to his side and convinces him to serve him. They attack Asgard and come face to face with Odin. The Absorbing Man takes the powers of everything they throw at him and despite Thor's help, Odin is forced to yield his kingdom and scepter to Loki. Yet while the two villains fight over the possession of the scepter, Odin sends them both adrift into the vastness of space.
Loki earns the gratitude of the Storm Giant Ghan by saving him from Thor and his Asgardian warriors.
Loki convinces King Hymir to challenge Thor who will become the king's slave if he loses, but when Thor succeeds, the king accuses Loki of betraying him.
