The Avengers: Loki
The half brother and archenemy of the god of thunder, Thor. Loki grew up under the great shadow of Tho and under the assumption that he truly was an Asgardian. He was actually the son of Laufey, the deceased monarch of the Frost Giants who were enemies of the Asgardians long ago. When the old king of Asgard, Bor, fought the Frost Giants he followed a giant to a sorcerer of the their people that turned out to actually be a present day incarnation of Loki in disguise. He knew however that he would not be a match for Bor's power and instead caught him by surprise and turning him into snow. Bor's son, Odin, who saw the last of his father being blown away. Many years passed and instead of Odin attempted to rescue his father he decided to lead his fellow Asgardians while following his own dreams. This had Odin leading his people into battle against the Frost Giants. Odin sought out Laufey and slayed him in combat. Upon achieving victory, he found a small Asgardian-sized child who had been hidden away by Laufey in shame of his child being so small. Odin took him as his own and raised him on Asgard. This set forth the events leading to the eventually downfall of Odin as he never realized that the Bor that had been torturing him from the grave was actually an illusion created by the present day Loki. Loki was quite the illusionist, hence why he is referred to as the god of mischief and evil.
Loki grew up in the constant shadow of his brother Thor. Asgard favored Thor of Loki forcing him to become resentful. Asgardians preferred seeing great strength and tenacity in battle which Thor demonstrated in spades unlike Loki. His gifts were much different than his foster brother as he was a skilled sorcerer where he had a natural affinity to command great magicial forces. He hoped that one day he would be skilled enough in the art to become the most powerful god in Asgard and to destroy Thor. His skills also earned him the nickname as the "God of Mischief." His cheap parlor tricks began to grow over time into more malicious acts as his lust for power and revenge steadily grew while also becoming more apparent to everyone around him. This lead to a change in his nickname to the God of Evil. Over the centuries, Loki would attempt to take control over Asgard and to destroy Thor in the process. However, Thor and Odin would frequently derail his plans. Odin even got to the point that he magically imprisoned his adopted son into a tree, but of course you can't keep a god down forever.
I apolgize for the picture, but its the best quality I could find
Over the course of their lives, the step brothers would constantly clash as Loki always sought out ways to confront Thor directly or even indirectly. Loki sent Amora the Enchantress to put a wedge in his step brother's relationship with the human nurse Jane Foster, but mostly when Odin openly was against Thor's relationship. Most Asgardians wanted Thor to be with fellow Asgardian Sif. The Enchantress however was unsuccessful in breaking up Jane and Thor, thus Odin came to Earth to break it up himself. Loki was alone in Asgard and took the opportunity to take his place at the throne. In order to secure his position as king of Asgard, he set the giant Skagg and fire demon Surtur loose on Earth hoping that the two would be able to defeat Thor and Odin once and for all. Loki's plan of course failed and as punishment he was sent to serve the Trolls. Loki's next attempt to hurt Thor was to turn Odin against his prodigal son, which yet again back fired in his face. You would think a guy would take a hint right?
Loki's devious acts would eventually hit close to home as he attacked Earth. His schemes against Earth not only caught the attention of Thor but even Earth's superhuman stretch. Loki manipulated Bruce Banner's alter ego, the Hulk, into causing plenty of destruction which led to the formation of the super hero team called the Avengers. Making matters worse for the god of evil, Thor was one of the founding members of the team and Loki yet again would constantly find himself on the losing end of his devious schemes. Loki even went as far as appearing as a teammate of the Avengers when he took on the guise of Scarlet Witch. As the Scarlet Witch he attempted to break the team up from the inside, most notably Norman Osborn. Scarlet Witch's brother Pietro Maximoff raced around the world to find the Avengers as he wanted to see his sister again. With the inclusion of Pietro (Quicksilver), Loki began to see him as a problem in his grand scheme as he really believed him to be Scarlet Witch. Eventually he was found out only to promptly return to Asgard.