Johannes Cabal the Necromancer (Johannes Cabal Series)

Johannes Cabal, a brilliant scientist and notorious snob, is single-mindedly obsessed in heart and soul with raising the dead. Well, perhaps not soul--he hastily sold his years ago in order to learn the laws of necromancy. But now, tormented by a dark secret, he travels to the fiery pits of Hell to retrieve it. Sataon, who is incredibly bored these days, proposes a little wager, Johannes has one years to persuade one hundred people to sign over their souls or he will be damned forever.--From publisher's description.