Yep and also Shakin Stevens

I can see that now that you mention it but more so In their earlier days I always confused him with Steven Weber.

I think it's highly subjective.
In some ways Gary reminds me of a much more attractive Willem Defoe, especially in Santa Fe.
In some other ways he reminds me of Alan Rickman, mainly because they share the same kind of handsomeness that could reduce me to a stammering idiot in less than 5 minutes
Yet Gary can look very different in every movie, a single accessory (i.e. the glasses in Office Space) can change his face. Add that he's an incredible actor and he can turn himself into whatever he wants to, and he doesn't even need much make up. It's the voice, the way he moves. That's why he makes me think of very different people. But mainly he's himself and he's pretty unique.
Gummitch
KONG BITES HIS HEAD OFF in a PG 13 kinda way!

Gary looks very similar to Steven Weber and Christian Bale
Heather O'Rourke,Judith Barsi,Dominique Dunne,Sharon Tate,Paul Richard

I can definitely see how you'd think there's a resemblance. Marc Singer is fairer with blue eyes and blondish hair and Gary Cole has darker hair and eyes, but they do have similar features.
Yes, he does look a bit like Marc Singer!