Alright, trying something different here. This contest is about a genre of character, namely the nameless ones. Sometimes they get a nickname or another kind of "Person X"-like pseudonym, but we never learn their proper name. Obviously, we're talking major characters, not bit players. Preferably the main character. As usual, entries may not exceed 200x200 pixels and/or 1 Mb data, they must be safe for work, and I'll allow SF & F for this one. And let's go old school for the time being, one entry per user.
So is this in context of just within the show or movie world or does it include what the credits tell us?
Well, I'd say that's a bit of a grey area. If it's a name prominently displayed, like in the main title sequence of a TV show, then it's too much, but if it's just in the end credits which most of the audience doesn't read anyway, that's okay.
This work? Deep Throat, The X-Files Or would this be better? The Female Founder, Star Trek: Deep Space Nine
Both work, Deep Throat obviously isn't a real name, and the Female Founder was a major player who was never named. Which one do you want to go with?
I'd tell you to pick one, as there is only one entry per user, but The Bride from Kill Bill actually does not qualify, as her real name is revealed very prominently in Kill Bill, Vol. 2.