I’m thinking along the lines of Comic Book Guy on “the Simpsons.”
Yes, I know that the writers eventually gave this character a real name. But if you asked the random person on the street who “Jeff Albertson” is, they’d stare blankly; whereas if you asked who “Comic Book Guy” is, a large percentage of folks would know he’s a Simpsons character.
ANY-way, what characters are popularly known by a title or nickname, and either don’t have, or are not particularly well-known by a proper given name?
To start the list off, there’s…
Comic Book Guy
Sailor Guy
Bumblebee Guy
Crazy Cat Lady
Did the Cigarette Smoking Man from X-Files ever have an actual name given? Wikipedia doesn’t list one, but says he once answered to the name C.G.B. Spender, but says that was never verified as his actual name.
The narrator of Ralph Ellison’s The Invisible Man never reveals his name.
There’s “The Man with No Eyes” from Cool Hand Luke, but most of the characters in that move are know by nicknames of some sort, so maybe that’s not exactly what you had in mind.