In LoS Gabriel gained some his powers from Cornell, the Werewolf lord, Carmila, the Vamipre Lord, after killing them and using the relics which contained an essence of their powers. I guess the more he used them, the more it got absorbed into him and the more he became like them. His main powers however comes from Laura, who turned him into a vampire and eventually died in the process and from The Forgotten One from whom he got the demon powers and evil at the same time.
I don't think he had absorbed any powers from Satan though, cause they don't show it. Perhaps in this game, if it is in fact Satan who is crucified, he may somehow escape and try to exact revenge on Gabriel and Zobek way into the future as shown in the LoS ending. Or perhaps the 'new dark power' mentioned in his bio is Satan himself?
Nice idea Ames, But if I remember right, Trevor Belmont is a human, atleast in the original timeline. He can't be a vampire since the Belmont clan is a family of vampire slayers. Perhaps he may be the son of Gabriel before he was turned into a vampire. Still, it does not say if his wife marie and bore a child. Perhaps they may reveal that the brotherhood hid the child from Gabriel or something in LoS2 due to some prophecy. Alucard could be the son Gabriel had with another wife, after he became a vampire.
All this is really ironic but interesting at the same time lol. Two lines of families started by one person who become born rivals for centuries to come.