Most of us watch a show or play a game and think, "This character is bae. I want to touch myself to rule 34 porn of them."
Occasionally, it'll happen the other way around. I'll discover a character that's been rule 34'd, finish myself off, then actually read up on canon material.
Most recent one is

lady_maria_of_the_astral_clocktower

rule34.xxx/index.php?page...of_the_astral_clocktower+

What guy, gay, or monster have you discovered through rule 34?

A lot of League of Legends characters, definitely. Specifically Headmistress Fiora, whom I still haven't played despite having started playing the game by now.
rule34.xxx/index.php?page=post&s=view&id=2959410

But the character who definitely takes this prize home for me is Yorha Number 2 Type B.
rule34.xxx/index.php?page=post&s=view&id=3105929
Never before have I seen a character and been so instantly turned on. Everything about her was so hot immediately. I masturbated to her many times before I ever actually picked up Nier: Automata. And now it is probably one of my favourites.
Oh and of course with all the new context I can think of scenarios so much better and masturbate to her even more.

Kantai collection