Mister X or Mr. X is commonly used as a pseudonym for someone whose name is secret or unknown.

Mister X may refer to:

• Mister X (Marvel Comics), a supervillain in the Marvel Universe
• Mister X (Vortex), the protagonist in Dean Motter's comic book series of that title
• The Amazing Mr X (comics), Britain's first superhero, who first appeared in The Dandy comic in 1944

• Mr. X (Resident Evil), antagonist first appearing in the 1998 video game Resident Evil 2
• A villain in the video game series Streets of Rage
• The villain in the video game The Ship
• The final villain in the video game Kung-Fu Master
• The pseudonym of Dr. Wily in Mega Man 6
  • Xander Payne, a character from the Mega Man Archie comics
• The pseudonym of Olga Gurlukovich during the Big Shell Incident in Metal Gear Solid 2: Sons of Liberty

• Mister X (1958 film), a 1958 Soviet musical film directed by Yuli Khmelnitsky
• Mister X (1967 film), a 1967 Italian superhero film directed by Piero Vivarelli also known as Avenger X
• Mr. X (1987 film), a 1987 Bollywood sci-fi film starring Amol Palekar directed by Khwaja Ahmad Abbas
• Mr. X (2015 film), a 2015 Bollywood sci-fi film starring Emraan Hashmi
• Mr. X, a recurring puppet on The Canadian Howdy Doody Show
• Mr. X, a recurring arch-criminal of comic Arabic films played by Fouad el-Mohandes
• Mr. X, in the animated series The X's
• Mr. X, a villain in the anime series Lupin III
• Mr. X (Simpsons), Homer's pseudonym in The Simpsons episode "The Computer Wore Menace Shoes"
• X (The X-Files), a character in the television series The X-Files
• The Amazing Mr. X, a.k.a. The Spiritualist, a 1948 thriller film
• Mr. X, the main character in the 1940s and 1950s radio and TV series The Man Called X
• Mr. X, an assassin in the 2008 film Wanted, played by David O'Hara
• Mr. X, a character who appears in the Fringe episode "Lysergic Acid Diethylamide"
• Mr. X, the pseudonym for Goofy in the animated short Aquamania
• Mr. X, a Teenage Mutant Ninja Turtles character associated with Mondo Gecko
• The placeholder name the farmer is given when he gets amnesia in the Shaun the Sheep Movie
• Mr. X, a secondary character in Big Time Rush
• Mr. X (Amphibia character), a character in Amphibia
  • "Mr. X" (Amphibia episode), the character's eponymous debut episode

• Mister X (band), a street punk group from Belarus
• "Mr X", a song by Ultravox from their album Vienna
• "Mr X", a song and single by Pauline Murray And The Invisible Girls
• Mister X, a character in the operetta Die Zirkusprinzessin (The Circus Princess) by Emmerich Kálmán
• Mr.X, American DJ also known as Afrika Islam
• Mr. X, mystery music composer of the film Enai Noki Paayum Thota
• Mr. X, drummer formerly in the band The Meatmen
• Mr. X, a character from God in Three Persons

• Donald Graves (Kremlinologist) (1929–2008), U.S. State Department analyst, from the 1982 Washington Post article "The Secret Files of Mr. X"
• George F. Kennan (1904–2005), American historian, in his essay "The Sources of Soviet Conduct"
• Carl Sagan (1934–1996), American astronomer, in an essay on his experiences with marijuana
• Norman Wexler (1926–1999), American screenwriter, in Bob Zmuda's Andy Kaufman Revealed
• Gaston Defferre (1910–1986), French Politician, using this pseudonym during the 1965 Presidential Elections
• Ben Zygier, a prisoner who was held in Israel
• The former longtime boyfriend of American radio talk show host, Robin Quivers

• Aeros Mister X, a Ukrainian paraglider
• "Mr. X", nickname of American golfer Miller Barber (1931–2013)
• Mr. X, a masked professional wrestler in the 1930s and 1940s, one of the identities of Cyclone Mackey
• Mr. X, a masked professional wrestler in the WWF in the 1970s, one of the identities of Jerry Balisok
• Mr. X, a masked professional wrestler in the WWF in the 1980s, one of the identities of Dan Marsh
• Mr. X (Straub novel), a novel by Peter Straub
• Mr. X, a player character in the board game Scotland Yard and its spin-off, Mister X
• Mister X, an alias used by Mayuka Kondō in the manga and anime series, Oniichan no Koto Nanka Zenzen Suki Janain Dakara ne!!

• Doctor X (disambiguation)
• Miss X (disambiguation)
• Professor X (disambiguation)
• Nomen nescio (often abbreviated as N.N.)
• John Doe
• X (disambiguation)

This disambiguation page lists articles associated with the title Mister X.
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