For a long time I thought stars you could recognize through imitation had vanished. I mean, no one ever did a Robert Redford imitation, and they don't do Kevin Costner or Brad Pitt either. They were no Cagney or Bogie, impression-wise.
But then people started doing Christopher Walken, and you could believe that we had at least a few stars you could "get" instantly.
This is a funny clip with Kevin Pollak, who not only does the best Shatner ever (starting at about 1:45), but manages to include 80s actors you'd never think of anybody doing, like Christopher Lloyd, but who are unmistakable. (There's also
this great NSFW clip with Pollak doing Albert Brooks trying to tell the Aristocrats joke but tearing it apart as he does it.)
I guess, if you think about it, who ever did Spencer Tracy? Or Burt Lancaster or Paul Newman? Some can be imitated, some can't, I guess.