Wolfspider
Explorer
Pbartender said:If D20 Modern had Tiefling Warlocks...
He is the unholy progeny of a witch and the devil Sheol. He was summoned to earth by Nazis bent on destroying the world. He was raised by a benevolent secret organization that gives him missions to combat supernatural evil. He is exceptionally strong and resilient (high Str and Con scores). He has other superhuman abilities that "stem from his demonic nature". His right hand and forearm is an oversized fist of stone that hits like a sledgehammer and he carried an immense pistol made from church bells and fragments of the true cross that shoots "really big bullets" made of holy water, silver shaving, garlic and other stuff specifically meant to harm supernatural creatures (together, the fist, pistol and special bullets all count as his eldritch blast).
Likely, he's multiclassed with a martial class, such as Fighter or Barbarian.
He didn't make a pact with the Devil in order to receive his powers. He was born that way. His demonic nature is best represented by his race, not his class. From your description, I think that he'd be best described in game terms as being a half-fiend human paladin.