There are an infinite number of possible Hulk's, this was talked about during Paul Jenkins run. The versions of Hulk seen so far are Green Hulk
(rampaging, not the brightest), Grey Hulk
(Joe Fixit, smart but weaker), The Professor (Best of the other 2), Devil Hulk
(Killer and very devious), Green Scar(Best version ever!!!!) and the often forgotten version of when Banner could turn into Hulk at will Green version, while maintaining his intellect. Peter Davids run on Hulk is a must read for all new Hulk fans, then Paul Jenkins followed by Greg Pak.
Jeph Loeb Color Books = Tracing
Collector: Hey man. If somebody draws something
and then you draw the same thing right on top of it, not going out-side the designated original art, what do you call that!
Little kid:I don't know. Tracing?
Collector:(to Banky) See?
Banky: It's not tracing.
Collector: Oh, but it is.
Banky:(to Little Kid) Do you want your book signed or what?
Collector: Hey - don't get all testy with him
just because you have a problem with your station in life.
Banky: I'm secure with what I do.
Collector: Then say it - you're a tracer.