So I’m watching an old episode of Sanford & Son on TVLand and I see that schticky guy who turns around real fast and says, “Eh-Yesssss?”. I remember he was something of a regular guest cast member on S&S, but what’s his name and what is he from originally? TV? Movies? Vaudeville?
He seems like the type of character that would have a lot of websites devoted to him, but I don’t know what to search for…
Sounds like Frank Nelson, who was a staple on The Jack Benny Show. I wouldn’t have imagined him on Sanford & Son, but IMDb says it’s so.
Yep, I remember the episode. He also made a cameo on SNL, and I THINK maybe All in the Family.
They also had a guy do that a few times on the Simpsons, and I also wondered who it was.
Frank Nelson: ‘Eh-YESSSSSSSSSS?’
Homer: Why do you talk like that?
FN: I had a Strooooooooke 
After I posted this I tried doing a search on ‘the yessssss guy’ on Google and I actually got the page Scarlett67 linked as a hit (lucked out with the number of 's’s I used!)
A lot of great info on that guy’s page. In particular, the story he tells about how, after admiring Frank Nelson’s work for so long he wrote a character in a cartoon just for him, but his producer still insisted that Nelson audition for the part rather than just hiring him outright. When he came to the studio to audition, the guy went into the waiting room to get him. When he approached him and asked, “Mr Nelson?” he replied (wait for it…)
“YESSSSSSSS?”
All the other voice actors waiting to audition for other parts all immediately recognized him and applauded!