Now I Nerd my ABCs

Ash
Buffy
?
Doctor Who
Edward Scissorhands
Frodo Baggins
Greedo
Harry Potter
Indiana Jones
The Joker
Kato
Luke Skywalker
Malcolm Reynolds
Nero
?
Peewee Herman
?
The Rocketman
Dana Sculley
The Terminator
?
Voldemort
?
Xena
Yoda
?

C is Constantine
Q is Prof. Quirinus Quirrell from Harry Potter
W is Wesley Crusher from Star Trek: TNG
I still need help for O, U, and Z. My guess for U is Ultron, but not sure if it’s right.

O is Odin, U is Ultraman (Japanese robot). Z???

Z is(Dr.) Zaius, Planet of the Apes

“C” is Castiel from Supernatural.