heh Beta Ray Bill is his name, he's an Alien Cyborg. He's a Walt Simonson creation who was worthy of Mjolnir and Odin gave him his own Hammer to help protect Bill's Race.
His race is the Korbinites. They're all gone but one extra who Galactus just recently brought to life for BRB. Check out Beta Ray Bill Saga of Stormbreaker. The story happens just AFTER Thor volume 2 ended.
here's a bit of history
Basically BRB is supposed to be a Cosmic version of Thor.