Darkness, Volume 3: Original Sin
Mafia hitman Jackie Estacado was both blessed and cursed on his 21st birthday when he became the bearer of The Darkness, an elemental force that allows those who wield it access to an otherworldly dimension and control over the demons who dwell there. Forces for good in the world rise up to face Jackie and the evil his gift represents, but there is one small problem in this story... they are the bad guys.
Collecting The Darkness Vol. 1 #15 - 25.