X The Thing That Lived
X-23
X-51

(Aaron Stack)
Gender: ♂
Alias of: Machine Man
Alternate version(s): Machine Teen, X-51 (Earth MiniM)

Features
Earth X ½ (Wizard Publication) ½.FT

X-51 (Earth MiniM)
Xakku

(Master Scout)
Individual of: Guna

Xandarian Worldmind
Xandarians
Xandu
Xantareans
Xantha
Xaos

Daniel Dash (Chaos)
Gender: ♂
Member of: X-Men II

Xartans
Xarus

Xarus
Gender: ♂
Parent(s): Dracula

Features
Vampires: The Marvel Undead 1.FT

Charles Francis Xavier (HouseOfM)

Gender: ♂
Alternate version of: Professor X
Universe/Dimension/Timeline: Earth House of M

Charles Xavier (XtX)

Gender: ♂
Alternate version of: Professor X
Member of: X-Treme X-Men II

Xavier Institute for Higher Learning
Xavier's Security Enforcers
Xavier's Underground Enforcers
Xavin
X-Babies
X-Calibre
XCE

Member(s): Bishop
Universe/Dimension/Timeline: Earth Bishop's Future

X-Cell
X-Club
X-Corporation

Member(s): M II, Multiple Man, Rictor

X-Corps

Member(s): M II, Multiple Man, Siryn

X-Cutioner
Xemnu
Xemu

Universe/Dimension/Timeline: Unknown Universe/Dimension/Timeline

Xenith

Gender: ♀
Individual of: Strontians
Sibling(s): Gladiator II

Xeron

(Star-Slayer)
Gender: ♂
Individual of: Mobians

Xeronians
X-Factor I
X-Factor II
X-Factor Investigations
X-Force I
X-Force I (Alt)

Alternate version of: X-Force I
Universe/Dimension/Timeline: Unknown Universe/Dimension/Timeline

Features
X-Men: Millennial Visions 2.FT

X-Force II
X-Force III

Alias: X-Statix
Alternate version(s): X-Force III (Alt)
Member(s): Battering Ram, Bloke, Spike

Features
Marvel Poster Magazine 1.FT - 2.FT

X-Force III (Alt)

Alternate version of: X-Force III
Universe/Dimension/Timeline: Unknown Universe/Dimension/Timeline

Features
X-Men: Millennial Visions 2.FT

X-Force IV
X-Force V
X-Humed

Member(s): Changeling

Xixix