Gabriel is a tortured soul, a lonely and angry child in an adult body. He can best be described as a vicious, unfeeling psychopath, but in reality he just wants to kill the pain and get rid of the “voices”—or prayers that he hears— that torture him nonstop. So he simply kills not for fun, but with purpose, although his anger and desire for revenge also causes him to “play” or “toy with” his victims cruelly before killing them. He is not to be underestimated. He approaches serial killing like an overachieving workaholic devoid of mercy. He has lost much of the power of speech and has become more of a mindless, wordless killing machine, saying very little if any in very few words, seemingly incapable of any feelings, or the concept of right and wrong. He grew up with nothing but pain and suffering and violence and death. And that is all he has ever known.
Despite his animal-like mindset, Gabriel is ambitious, determined, smart, and practical and determined to do one thing and do it well—serial killing.
It’s revenge and the aching pain of loneliness that drives him. When the “voices” come, it literally drives him insane and activates his impulse to kill. He hates his existence and his “job, and he hates being “chained” to his role. He does everything he can to rebel, and sees becoming a Vampire as a way out, so God cannot control him anymore since he has become evil, but it does not silence the prayers. Ironically, he does need the prayers to home in on his "food"--humans.
But he is in a way redeemable in that he has some remnant of feelings, and seems to have a soft spot for the author Ms Price, who he has seen in Jeromos’s monastery. And he is drawn to her because he secretly wants stability and devotion he never had and never had a chance to experience companionship. But it’s not love—it’s more about having something that can “soothe” the anger inside him. He knows he needs her in a more practical manner though—to regenerate and heal, because he knows she has that power. But he takes some time to act on planning to take her, since some part of him is loyal to Jeromos for saving his life. So he does retain somewhat of a conscience.
But he is selfish too—he’s mainly concerned about his own future and security that is why he is a loner and creates his own marble army, which must be made of supernaturally-charged inanimate objects--statues--, and cannot be made up of Vampire Guardian Angels or humans because he does not trust them and he cannot relate to them. He’s something like a socially awkward, aloof serial killer, distant and not easily approachable or easy to reason with. He can play a great actor though, as he seduces only to kill and eat, with little words and a charming personality that humans can see as he hypnotizes them with his gaze. But that is the extent of his interactions. And he does not bother with any type of interaction with humans, vampires or angels. He is singularly focused on one thing: he will do anything to reach his goal of killing Joseph and Cameron, anyone who gets in his way, and getting rid of the praying voices in his head and the people who pray. He is completely obsessed with his goals.
And in the war between the Vampire Guardian Angels, surprisingly, despite being the most powerful of them all, he has absolutely no desire for power, no desire to be king, and just wants to be left alone. He just wants relief from all the pain and prayers, and will find any way to soothe himself and find relief from them, whether it's killing or anything else, which is also why he wants the author, that makes him feel better, even for a few moments.
He is remarkably resilient despite all the injuries he has sustained. He will weather any bad times just like he did as a child in his past life, and any setbacks with patience and perseverance. He takes risks such as coming down from Heaven without the portal because he is willing to risk it all to get his revenge. But there are times when does play it safe though—he plans, observes and evaluates what the cost of his action is, and if he can come out of it in one piece.