Born with a nerve disorder, Barry Bauman was basically a vegetable with none of his senses. This left Barry in his own world where he soon began to discover his own mind, eventually using 100% of his brain. He developed psychic powers and took control of his nurse, Tom Vocson.
He grew resentful of the people of Earth and learned to project his mind across space. He launched an asteroid toward Earth and even began hiding stars in pocket dimensions created from his mind - thus giving himself the name Star-Thief. In the process, he gained the attention of Adam Warlock
and used him for his amusement, holding back his massive powers to keep himself occupied. This resulted in him losing control over Vocson who shot his defenseless body in the head.
But the death of his physical body did not kill Barry and it appeared that his soul was taken into Warlock's Soul Gem
But he did not go to the Soul World. Instead, he hopped from host to host until arriving at the mental asylum known as Halfworld
. Rocket Raccoon
and the security of the facility found a way to lock him up deep in it's center.