A form of Names to Run Away from Really Fast: Some people end up going by a pseudonym where they have a one-word description followed by an X. It's generally not a good idea to press them for real names.
Anime & Manga
- One Piece has an inverted example in X Drake (though the X is pronounced "Diez", as in the Spanish equivalent of "10", which "X" is the Roman numeral for).
- The titular mech from After War Gundam X also counts.
- Marvel Comics, who publish X-Men, has Professor X, Weapon X, Agent X, and Mutant X.
- From Godzilla: Final Wars, we have the last monster Godzilla fights, named Monster X. Unlike the other kaiju in this film, Monster X puts up a great fight. ...And then he turns into Kaizer Ghidorah and turns the tide of the battle in his favor...
- Devoted members of the Audubon Ballroom from Honor Harrington use "X" as their only last name; special mention goes to Jeremy X. Definitely run from the Ballroom if you're associated with the slave trade.
- CSI: NY had a storyline about a female Professional Killer who they only referred to as "Suspect X." Her crimes included killing an Internet celebrity to take her identity, assassinating a federal judge, holding hostage, surgically altering and finally killing a random innocent woman to fake her own death, and hacking Second Life.
- While Mega Man X himself is a heavy aversion in the games proper, he does have an evil counterpart from the Megamission card game, "Mega Man iX". And then there's Copy-X to consider...
- Longshoreman X (yes, really) is a boss in the original Dead to Rights. He fights with full fisherman gear and a spear gun.
- Cave Story has a rather infamous boss called Monster X.
- In Kingdom Hearts II, the only real "boss" in the Gummy Ship Missions is called Hunter X, found only in the very last mission on the hardest difficulty.
- Gaia Online has Labtech X.
- Red X; not just the only antihero in the series but also the only character to never be defeated! (from the animated Teen Titans, with a color to boot!)
- Beast Wars gives us Protoform X, complete with a big ugly X on his stasis pod. Prior to getting sealed in that stasis pod, he was on a massive spree of murder, destruction, and cannibalism, with a special focus on destroying everything Depth Charge ever cared about. Later receives the name Rampage once released from his stasis pod and forcibly recruited by Megatron.
- Malcolm X, why not. Real life Badass Preacher extraordinaire, not to mention (at least from his own perspective) an epic HeelFace Turn when he left the black separatist Nation of Islam for mainstream Islam.
- There is an as of yet unidentified pliosaur known as Predator X. Estimates put its length at about 50 feet and give it a bite force more powerful then a Tyrannosaurus rex.
- Planet X
- Angelspit's DestroyX.