Gabriel Tosh is one of the Hyperion's crew in StarCraft 2: Wings of Liberty. He is there serving with Jim Raynor, Tychus Findlay, Matt Horner and other crew members. It is belived he a is very gifted Terran with powerful psionic abilities.
Gabriel grew up with his mother in the slums of Haji. Since he was young, he believed that his great psionic powers were voodoo magic. Tosh was later conscripted into the Confederate armed forces. People, who are highly trained to find such gifted men and women found Gabriel and then he realised, he had real psionic powers.
After that, Gabriel Tosh disappeared and no one heard of him since. But there were rumors, that Gabriel joined some kind of top secret government organization, where he could find some use for his psionic skills.