Loki Odinson was the biological child of
Laufey, the
King of Jotunheim, who was abandoned and left to die shortly after his birth. Found by
Odin, Loki was taken to Asgard and raised by him and
Frigga as an
Asgardian prince, along with his adoptive brother
Thor.
When Thor was to be crowned King, Loki sabotaged the coronation by letting
Frost Giants attack
Asgard, thus leading Thor to seek vengeance on
Jotunheim, which resulted in Thor's banishment to Earth and Loki finding out the truth about his heritage.
Frigga gave Loki the throne when Odin fell into the Odinsleep; however, when the
Warriors Three and
Siff attempted to return Thor home, Loki was forced to try to stop them. Regardless, Thor returned from his exile on Earth and ended Loki's reign. With Odin disapproving of his actions, Loki allowed himself to fall through the deep abyss of space, entering a wormhole created by the sudden termination of the
Bifrost.
He was found by
Thanos's Armies, and pledged his alliegance to
Thanos who gave him the
Sceptre (making him briefly a
Stonekeeper) to aid in him his planned
invasion of
Terra to retrieve the
Tesseract and (presumably)
Eye of Agamatto.
After the failure of his invasion, he was inprisoned in the dungeons of
Valaskjalf until the
Second Dark Elf War, when he aided his half brother and eventually faked his own death in battle.
In the original timeline, Loki then usurped Odin as All-Father, eventually leading to the destruction of Asgard by
Hela.
In the new timeline he fled to earth, not wanting to usurp his mother, taking the
Aether with him for safekeeping. He was discovered during Fear Itself, and the Aether was taken to be studied by
Avengers Idea Mechanics (where it would eventually end up in the hands of
Michael Kovaks).
As punishment for the theft, Loki was appointed to the empty Asgardian seat on the
Council of Realms to serve his sentence in service to the
Asgardian Empire.