Namor (/ˈneɪmɔːr/), also known as the Sub-Mariner, is a character appearing in American comic books published by Marvel Comics. Created by writer-artist Bill Everett for comic book packager Funnies Inc., the character first appeared in Motion Picture Funnies Weekly #1 (uncirculated). Namor first appeared publicly in Marvel Comics #1 (cover-dated October 1939). It was the first comic book from Timely Comics, the 1930s–1940s predecessor of Marvel Comics. During that period, known to historians and fans as the Golden Age of Comic Books, the Sub-Mariner was one of Timely's top three characters, along with Captain America and the original Human Torch. Moreover, Namor has also been described as the first comic book antihero.

The mutant son of a human sea captain and a princess of the mythical undersea kingdom of Atlantis, Namor possesses the superstrength and aquatic abilities of the Homo mermanus race, as well as the mutant ability of flight, along with other superhuman powers. Throughout the years he has been portrayed as an antihero, alternating between a good-natured but short-fused superhero, and a hostile invader seeking vengeance for perceived wrongs that misguided surface-dwellers committed against his kingdom. A historically important and relatively popular Marvel character, Namor has served directly with the Avengers, the Fantastic Four, the Invaders, the Defenders, the X-Men and the Illuminati as well as serving as a foil to them on occasion.

Tenoch Huerta Mejía portrays Namor in the Marvel Cinematic Universe (MCU) films Black Panther: Wakanda Forever (2022) and Avengers: Doomsday (2026).

Namor was created by writer-artist Bill Everett. The character first appeared in April 1939 in the prototype for a planned giveaway comic titled Motion Picture Funnies Weekly, which was produced by the comic book packager Funnies Inc. The only eight known samples among those created to send to theater owners were discovered in the estate of the deceased publisher in 1974. Allegedly, Everett created Namor because he was informed that Carl Burgos had created the Human Torch, who can manipulate fire, and he wanted to play on the notion of "fire and water". His interest in "anything nautical, [and having] to do with the sea", also factored in Namor's creation and origin.

Everett stated that the inspiration for creating the character was Samuel Taylor Coleridge's poem The Rime of the Ancient Mariner (1798), and came up with "Namor" by writing down noble-sounding names backwards and thought Roman / Namor looked the best. He described the character as an "ultra-man of the deep [who] lives on land and in the sea, flies in the air, [and] has the strength of a thousand [surface] men". When the giveaway idea with Motion Picture Funnies Weekly fell through, Everett used the character for Marvel Comics #1, the first comic book by Funnies, Inc. client Timely Comics, predecessor of Marvel Comics. The final panel of the earlier, unpublished eight-page Sub-Mariner story had included a "Continued Next Week" box that reappeared, sans lettering, in an expanded 12-page story.

In his first appearances, Namor was an enemy of the United States. Comics historian Les Daniels noted that "Namor was a freak in the service of chaos. Although the Sub-Mariner acted like a villain, his cause had some justice, and readers reveled in his assaults on civilization. His enthusiastic fans weren't offended by the carnage he created as he wrecked everything from ships to skyscrapers." Everett's antihero would eventually battle Carl Burgos' android superhero, the Human Torch, when in 1940 Namor threatened to sink the island of Manhattan underneath a tidal wave. When the U.S. entered World War II, Namor would aid the Allies of World War II against Adolf Hitler and the Axis powers. Supporting characters included Betty Dean, a New York City policewoman introduced in Marvel Mystery Comics #3 (and later known as Betty Dean-Prentiss), who was a steady companion, and his cousins Namora and Dorma.

Namor starred in the Golden Age comic book Sub-Mariner, published quarterly, then thrice-yearly, and finally bimonthly, from issues #1–32 (Fall 1941–June 1949). A backup feature each issue starred the detective-superhero the Angel. Along with many other Timely characters, Namor disappeared a few years after the end of World War II and the decline in popularity of superhero comics. He briefly fought crime as a member of the post-war superhero team the All-Winners Squad, and, through a 1970s retcon, was given a history of having fought with the Allies during World War II in the superhero team the Invaders. Both of these super-groups were built around the core of Namor, Captain America, and the original Human Torch. The Sub-Mariner experienced a brief revival in the mid-1950s at Atlas Comics, the 1950s iteration of Marvel. Along with Captain America and the original Human Torch, he was revived in Young Men #24. Soon afterward, Sub-Mariner was revived with issues #33–42 (April 1954 – Oct. 1955). During this time, Namora had her own spin-off series. A planned live-action television program starring Namor did not appear and the revival of the comic book series was cancelled a second time.

Namor returned in Fantastic Four #4 (May 1962), where a member of the titular superhero team, Johnny Storm, the new Human Torch, discovers him living as an amnesiac homeless man in the Bowery section of Manhattan. Storm helps him recover his memory, and Namor immediately returns to his undersea kingdom—later identified as Atlantis in Fantastic Four Annual #1 (June 1963). Finding it destroyed from nuclear testing, Namor assumes his people are scattered and that he will never find them. He again becomes an antihero during this period, as two elements – a thirst for vengeance and a quest for identity – would dominate the Sub-Mariner stories of the 1960s. He was both a villain and a hero – striking against the human race who destroyed his home, but showing a great deal of noblesse oblige to individuals.