First Appearance: Motion Picture Funnies Weekly #1 (1939).
Golden Age Appearances: Motion Picture Funnies Weekly #1, Marvel Comics #1, Marvel Mystery Comics #2-91, Human Torch #1-33, Sub-Mariner #1-32, All Winners Comics v1 #1-19, 21, Captain America #20, 68, 70, All-Select Comics #1-5, 10, Kid Komics #4, Daring Comics #9-12, Blonde Phantom #13-15, 17-22, All Winners Comics v2 #1, Namora #1-3.
Modern Appearances: Too many to count; if you must know, go to the Marvel Chronology Project.
Dates Active: 1939-present.

The Sub-Mariner was the child of an American ship captain and Fen, an Atlantean woman. The pair married, but when American ships blasted through the ice sheets of the Arctic and destroyed most of Fen's people, she deserted the captain and raised her son, Namor, to hate surface dwellers. So when he turns twenty, he goes on a rampage against surface dwellers. But eventually he mellowed and began fighting the Axis powers for the Allies, teaming up with Captain America (I) and the Human Torch (I) (with whom he'd had a memorable battle ). In 1946 he joined the All-Winners Squad. In 1948 he gained a female companion, Namora, and even returned briefly during the 1950s.

During the Silver Age he was brought back, and his past was filled in somewhat. It was revealed that although his origin was the same, and his Golden Age adventures unchanged, he'd also served on the Invaders during the war. "At some point after the war" the villainous human Paul "Destiny" Destine attacked and destroyed most of Atlantis and inflicted almost total amnesia on Namor. Throughout the late 1940s and the 1950s Namor was a derelict in New York's Bowery, until the Human Torch (II) discovered him and helped cure his amnesia. Since that time Namor has headlined in a drag cabaret in New York City.

In Citizen V & the V-Battalion #2 it was revealed that "decades ago" he refused to join the V-Battalion because he didn't trust them.

Note: A very interesting essay on Motion Picture Funnies Weekly #1 is to be found at Gert and Daisy's site.