Voice are always enhanced when you can add a visual effect. I know someone who does a reasonable Groucho voice, greatly enhanced by eyebrow motion and a pretend cigar.
Some voices have simple vocal techniques that have been mentioned. There are a bunch that are based on speaking through clenched teeth, Beavis is one, Edward G. Robinson also. He’s been imitated so many times people recognize the mannerism even if they don’t know who is was. Just talk through clenched teeth and end every sentence with an extended “seeee”.
I do Butthead the way Mike Judge said he did it. It’s a voice that comes from deep down, way below the diaphragm. Let any sense of motivation and will leave your body, slowly utter the words followed by the least emotional chuckle possible. I don’t know how I do it, but I can do the Boris Karloff part in Monster Mash. I have a deep voice already, there’s something about over enunciating the words or something.
I remembered that I do a good Gregory Peck and didn’t think anyone had done one. YT proved me wrong. Plenty do from Rich Little 50 years ago to Seth McFarlane.
Edward G. Robinson has kind of become the default “old-timey gangster” voice. As with many frequently-imitated people, most people aren’t really doing an impression of the actual person. They’re doing an impression of other impressionists.
Like when you “do” Shatner, you’re really doing Kevin Pollak doing Shatner. When you do Bela Lugosi, you’re really doing some long-forgotten nightclub comedian doing Lugosi.
When I do Lugosi I’m doing Lugosi based on his films. However, even Shatner is doing a Kevin Pollak impression of Shatner because nobody… really… talks!.. that!.. way!.
