Phat (William Robert "Billy-Bob" Reilly) is an openly gay fictional character, a mutant in the Marvel Universe. He was created by Peter Milligan and Mike Allred in X-Force vol. 1 #117 (2001). Phat's mutant power is the ability to expand the fat deposits in his body, making his body larger and fatter.
Phat grew up poor and involved in the gangster life. At first his powers manifested as simple weight gain, which he put down to the stress of his life. Once it became clear he was a mutant, he trained well and used his abilities to fight crime, even before joining X-Force. Once rich, he tries to give his family what he never had growing up. He gave them a house, but they still lived in an RV, preferring the closeness.
Phat's first outing results in a fight with the old X-Force, who did not agree to the use of the name or the methodology of the team. His first mission sees the death of two his teammates, Saint Anna and Bloke. Bloke would not be the first gay member of the team.