I'm not familiar with all, or even most, iterations - but it seems like everywhere I turn in contemporary horror lit, there's a Constantine rip-off. I get the fascination, I like the character, but how many authors are going to try to squeeze into that clown car before the audience yawns more than it buys?
I may be off base in my assumption that Constantine popularized the idea of a damaged magician gumshoe (hesitant damned occult hero/anti-hero), but he's the most prominent example I'm aware of.
I wonder what comes next? I'm eager to find out.