Joe Cocker. Not sure what I thought he’d look like, but wow. Not like that.
That is surprising to me too. I always pictured him like a more macho Frankie Avalon, which isn’t far from Paul Anka.
He relates an anecdote about that. Starts at about 5:00, but the rest of the interview is good too.
13 year old me:
“Hootie’s black? You’re making that up!”
Laura Brannigan. Back when her first single came out (pre-video) we had pretty much immediately dropped her into the “scuzzy synthesizer dance queen” category.
Gabriella Cilmi singing “Sweet About Me.” I didn’t think she was a little white girl.
As a child I thought Creedence Clearwater Revival must have been black too.
Does that make me terrible?
Aaron Neville. One of the sweetest male singing voices ever. I expected him to look something like Michael Jackson. But he’s built like a longshoreman.
I figured a group called The Troggs who sang a song like Wild Thing would be from the psychedelic, scraggly-beard, 60’s, not the clean-shaven, matching-suits 60’s.
Anyone who listens to old time radio shows will have a lot of these. I was probably most surprised by Dennis Day, who didn’t look much like the naive adolescent he played on radio. See also Ezra Stone as Henry Aldrich.
If a radio DJ counts, then “Cousin Brucie” Morrow, who has appeared in a few films such as “Dirty dancing”. I had pictured him as a short, dark haired chubby guy, probably because a classmate named Bruce was such a body type. Morrow looks to be tall, lean, brown hair type.
I remember my sister being shocked when she saw Gary Puckett of the Union Gap on TV—“But he’s so…ugly!!!”.
Well, maybe Brown-eyed Schmaltz, but it doesn’t have the same ring to it… 
Charlie Patton.
How could that face, on that body, with that guitar, make those sounds?
Fred Travalena used to have a joke where he’d imitate Wayne Newton. He’d sing a few lines of “Danke Schoen . . .” and sound just like Wayne. Then he’d announce his Brenda Lee imitation.
“Danke Schoen . . .”
Listening to “Into the Mystic” or even “Moondance”, even if you knew Van Morrison was Irish, you wouldn’t really picture a pastier, doughier, Meatloaf, would you?
My first awareness of these people was from the radio. When I first saw images of them, it was like “No way!”
Gregg Allman
Arthur Godfrey
William Conrad (Gunsmoke)
Frank Sinatra
I don’t recall what my mental image was of the singer of “Karma Chameleon” back in 1983. But I know it wasn’t anything like the reality.
It’s even harder to imagine this guy singing it.
I remember my mom showing me a picture of Bonnie Tyler back in her “It’s a Heartache” days. Not how I would have pictured her.
Steve Tyrell wasn’t what I was expecting after hearing him on the radio.
I thought the lead singer of Rush was female until I looked them up on YouTube.