That's not Groucho and that's not Ed Sullivan. Those are both photos of Will Jordan, maybe the best impressionist who ever impressioned. Among other comedians it is widely acknowledged that Jordan invented The Ed Sullivan Impression. It's the most-imitated imitation of all time, simulated by amateurs and stolen outright by professionals. Just about everyone who ever "did" Ed, apart from John Byner, was actually doing Will Jordan: The mannerisms, the facial contortions, the movements…even the phrases. People think of Ed as always saying, "We've got a really big shoe for you tonight." Well, Ed didn't say that. Will Jordan said that. (If Ed ever said it, it was because he was imitating Jordan imitating him. One of the amazing things that can happen with a great impression is that the real person starts to sound like the mimic. Happens all the time, just as every year our presidents are in office, they look a little more like the political cartoons.) Here's a video link to about half a minute of Will Jordan in Sullivan mode.
Another top impressionist told me that what he did involved a set of two or three skills. You needed to have the vocal and physical dexterity…that's all one skill. Another is that you need to have the "ear" to listen to the real person, pick out the extremes and know what to emphasize. It's a lot easier to "do" someone else if you hear a good impressionist "do" them…and it works the same way with cartoonists. A professional caricature artist once told me that the first time he had to draw Richard Nixon, it was more useful for him to look at a Mort Drucker drawing of Nixon, as opposed to a photo of the actual person.
The third skill — and this one is helpful but not mandatory — is the ability to do the impression and be funny. I see a lot of impressionists around who can sound like the guy and maybe look like the guy…but that's about it. Absent sharp material, all it is is a stunt. I always found Will Jordan very funny.
I'm really in awe of great impressionists. I have trouble sounding like me, let alone someone else. Recently, I heard from someone who'd read where I mentioned Will Jordan elsewhere on this site and thought I'd slighted the guy. I don't think I did. I think the fellow who wrote misread me. But just in case anyone else does, let me set the record straight. I am in awe of Will Jordan and wish we saw more of him.