Namor's father, American seaman Leonard McKenzie, embarked on an expedition to Antarctica in 1920. McKenzie's ship was searching for the Lemurian city rumored to house the mythical Helmet of Power at the behest of one of his passengers, Paul Destine. However, McKenzie distrusted the uses to which Destiny would put the Helmet and caused an avalanche to bury the city. Making his way to safety, McKenzie set explosive charges to break up ice floes in the ship's path, unaware that Atlantis lay beneath the waters.
The city sustained heavy damage, and Atlantean Emperor Thakorr commanded his daughter Fen to investigate the cause of the explosions. Startling McKenzie's crew, the blue-skinned princess wound up staying aboard the ship for several weeks. In a strange twist of fate, Fen and McKenzie quickly fell in love and were married. Thakorr, fearing his daughter had been kidnapped or killed, sent an Atlantean war party to search for her. Thinking her a captive, the Atlanteans slaughtered McKenzie's crew and apparently McKenzie himself. Afterwards, Fen returned with the War party to Atlantis. Nine months later, Namor was born the first known Homo sapien - Homo mermanus hybrid.
The young prince grew up with a short, nasty temper and a hostile attitude toward surface-dwellers, whom he blamed for the near-destruction of Atlantis. When Thakorr discovered men in diving suits near Atlantis, he assumed they were advance scouts for an invasion force causing the fiery Sub-Mariner to launch frequent pre-emptive attacks against humanity, causing untold destruction throughout New York City and leading him into confrontation with the original Human Torch. When Nazi troops attacked Atlantis, however, Namor joined the Allied cause alongside Captain America and his fellow Invaders.
Atlantis largely avoided the damage sustained by the surface world during World War II, but did fall prey to a series of severe earthquakes at war's end that destroyed much of the fabled city and Namor again was dispatched to New York, where he fell afoul of Paul Destiny, who had finally obtained the Helmet of Power and was causing the quakes. His power destroyed much of Atlantis, killing Thakorr and Fen. Under compulsion of the Helmet, Namor returned to New York with amnesia and became a wandering derelict.
Eventually, Johnny Storm, the second Human Torch, discovered Namor in the bowery. Burning away the extra hair and substantial beard Namor had grown, Storm dropped the Atlantean in the harbor. The immersion restored most of Namor's memory. Assuming humans had destroyed Atlantis, Namor rashly invaded New York to avenge the destruction of his homeland. Even after the survivors of the Atlantean civilization welcomed him as their rightful king, he stubbornly spent the next several years warring with the surface world, most often opposed by the Fantastic Four. In the midst of his campaign against humanity, Namor developed an attraction to Susan Storm, the Fantastic Four's Invisible Girl. In his regal arrogance, he has courted her for years, seemingly undeterred by Sue's relationship with Mister Fantastic. Though he later realized he couldn't have her, and focused his attentions instead upon his Dorma. Against the surface dwellers, Namor has teamed up with both Doctor Doom and Magneto, though both turned against him once they felt they had the upper hand. With the help of the Fantastic Four, Namor soon defeated both one-time partners.
Eventually, Namor realized he had to put aside his hatred for humanity for the good of his people and banned official acts of war against Homo sapiens. Namor even grudgingly began using his superhuman abilities to defense of the surface world. First and foremost, he was the monarch of Atlantis. As such, he was beholden only to his subjects. The Sub-Mariner was a founding member of the loosely knit group of heroes known as the Defenders, brought together with Doctor Strange and the Hulk when an ultimate computer called the Omegatron threatened Earth. However, a curse forced the original three Defenders and the Silver Surfer to part ways. The condemnation was lifted, but Namor did not return to the Defenders at that time. Even though they had saved the earth many times, Namor viewed his duties with this loose-knit band of Defenders a distraction at best. The team eventually disbanded, due to circumstances beyond their control. Later, the founding three Defenders and the Surfer were drawn together once again to battle the forces of evil.
For several years Namor was part of Illuminati, a group of influential super heroes who met secretly to share information. The meetings were kept secret because demands made by Namor. The Illuminati were eventually disbanded after some serious disagreements including but not limited to the fact that Iron Man wanted the Illuminati to support the super hero registration act but most of the others, including Namor, disagreed.