Actors that became famous by emulating other actors.

[Gothic Sponge]

Off the top of my head:

Alan Alda basically played Groucho Marx in M*A*S*H
Christian Slater = Jack Nicholson

He didn't become famous for it, but Jon Stewart periodically emulates Jackie Gleason and Woody Allen.

[Philostopher]

1. Personally, I'm convinced Chuck Connors

Had a career because of how much he resembled Kirk Douglas (not just physically -- his voice and bearing were also very similar). He never got the roles Douglas got, but he looked enough like him that he got a lot of B-movie roles playing characters Kirk Douglas could have played if he'd been a B-movie actor. B-movie directors might have wanted Kirk, but they could get Chuck Connors to play the role and dream about doing movies Kirk Douglas would accept.

[mitchum]

2. I buy that theory...

and I've always had a strange fondness for Chuck Connors (even have an autographed glossy)

[lpbk2713]

3. Jack Nicholson

I always thought he wanted to be another Brando.