Nick Fury asks Thor's aid in investigating an alien ship heading for earth; Thor arrives and triggers the awakening of an alien protector, Beta Ray Bill; Bill bests Thor and takes up his hammer only to be accidentally summoned to Asgard by Odin who thinks he is summoning Thor.
Thor: Odin, ruler of Asgard, and Gaea created a child of both Asgard and Midgard (Earth). Thor was taken to Asgard to be raised by Odin's wife, Frigga. On Thor's eighth birthday, Odin had the magical hammer Mjolnir created, to be presented to Thor once he proved to be a worthy warrior. Eight years later, he succeded and Odin present Mjolnir to Thor, declaring him the greatest warrior in Asgard.
Beta Ray Bill: As the fleet approached the Milky Way galaxy, it was detected by a S.H.I.E.L.D. sattellite. Nick Fury asked Thor to investigate. Thor was deemed a threate by Skuttlebutt, so Beta fought him. During the battle Thor was separated from his hammer, Mjolnir, and reverted to Donald Blake. Curious, Bill picked up Mjolnir and the hammer deemed him worthy, granting him the power of Thor.
Loki: Loki is one of several powerful beings from the magical realm of Asgard, who have been worshipped as gods. In childhood Loki greatly resented the fact that Odin and the other Asgardians favored the young Thor, who already had a nobility of spirit and excelled in all his endeavors. As a boy Loki began studying the arts of sorcery, for which he had a natural affinity.
Sif: Sif was born a second generation goddess of Asgard, her parentage unrevealed. As a child, she had golden hair and was on occasional playmate of Thor and his half-brother Loki. Once, while she was still an adolescent, Loki decided to play a trick on her in retaliation for her preference of Thor's company over his. As she slept, Loki cut off all of her golden hair.