Kristin Wiig is actually really good at several impressions. Her Drew Barrymore is hilarious.
I have no contribution to this thread other than to report that when I first saw the thread title, I thought it said Most Impregnated Celebrity?, which I thought was a really weird topic for a thread, even on the Straight Dope.
For women, I would say someone from the golden age of movies like Greta Garbo, Bette Davis or Lauren Bacall.
You know how to whistle don’t you?
I’d forgotten about him. So, there’s one, at least. 
There were a few who I remember seeing on TV during the 1970s, when impressionists were more popular overall – I had to do a little googling to find Marilyn Michaels’ name, but she was on TV a lot back then.
Tina Fey doing Sarah Palin.
Tracey Ullman doing everyone from Helen Mirren to Laura Bush.
Catherine Tate doing Queen Elizabeth II. (“Are you bovvered?”)
I suspect that most SNL cast members have a few impressions that they get fairly good at, as that’s part of the nature of the show – Tina Fey as Sarah Palin also comes to mind.
OTOH, modern female comedians whose acts are based on impressions are probably even rarer than male impressionists today.
Michael Jackson, for the dance moves and the “wooo!”
John Travolta, everyone disco dancing.
Santa Claus. You see 'em everywhere around Christmas.
I’m pretty certain that the reason comics don’t do impersonations any more is because celebrities have almost no recognizable mannerisms today. Can you really see anyone imitating Casey Affleck or Sam Rockwell or Jake Gyllenhaal? How would that be funny?
I’m no pro, but I can do a pretty funny Sam Rockwell. You squint your eyes a bit and talk out the front of your mouth. You do the face of Leo DiCaprio but you talk as a deeper and less vapid Owen Wilson
So you do an impersonation by impersonating somebody else badly? :dubious:
Hey: it’s been working for Rich Little for decades.
I’m getting sick of everyone attempting Tilda Swinton, Jeremy Irons, Mickey Dolenz, and Kirsten Dunst.
Enough already!
sheesh
ETA - My Ernie Johnson is killer.
Elvis first.
Charlie Chaplin and Groucho Marx are probably joint second.
I’d put Marilyn Monroe ahead of both of them, with her breathy voice, her mannerisms, and her singing ("Happy… birthday… Mister President…).
Are we calling it “impersonation” when someone just quotes a line in the celebrity’s distinctive speech patterns? That’s an impression, maybe, but not an impersonation. An impersonation includes at least some attempt at capturing appearance and mannerisms, too.
I’m inclined to agree with Peter Morris’ top three.
There are no more stars. There are generic actor men with generic ‘man faces’ (as are most generic women ‘stars’.) . They are all interchangeable. Little brown hamsters running on the wheel of Hollywood. I can’t tell one from another. I can’t think of ANY present day ‘actors’ who have one distinguishing characteristic. They are all drones in spandex in Spiderman and Batman and Avenger movies. All just…meat. Like cattle, like Alfred Hitchcock called them.
Preach it!!!
Has Alec Baldwin’s masterful performance as Trump stopped all other impressionists?
May impressionists seem to be rather thin on the ground. Likewise those doing other UK politicians.