He immediately vowed vengeance on the surface world and attacked it. The Fantastic Four were able to stop the Sub-Mariner, and he became instantly enamored of Sue Storm, a crush that he would carry with him for years. Namor also joined The Hulk in an attack on the Avengers, but was repulsed when the temperamental Hulk left the fight.
Shortly thereafter, Magneto approached Namor and asked him to join his first Brotherhood of Evil Mutants. Namor fought against the X-Men in a battle alongside Magneto, but refused to kowtow to the Master of Magnetism and ultimately rejected the offer.
Namor returned to Atlantis and was supposed to marry his cousin Dorma, with whom he had fallen in love. However, Llyra, an evil princess of Lemuria, another submarine culture, kidnapped and replaced Dorma at the wedding hoping to usurp Namor's kingdom in that way. Legally, though, Dorma was the one Namor had married, but he still had to find his wife. Unfortunately, Llyra had taken Dorma to the surface world in a tank as bait, and when Namor arrived, she smashed the tank to distract him. Namor was unable to save Dorma, and nearly went insane from grief.
Later on, Namor, flying near the Savage Land, spotted Magneto lying unconscious near a volcanic eruption (Magneto had just fought Sauron and several X-Men). He picked Magneto up and brought him to Atlantis to recuperate. Namor then left Atlantis to join the Fantastic Four on a mission, and returned to find that Magneto had usurped his throne. The FF and Namor made short work of Magneto, and Namor regained his kingdom.
Unfortunately, trouble brewed often for the Avenging Son of Atlantis, and his lost his kingdom a number of times. He also married the Alpha Flight member named Marrina, another sea-dweller, but lost her when she turned evil and was killed. During some of his exiles from Atlantis, he joined his former rivals the Avengers, and helped to found the Defenders. He also was a member of the short-lived undersea team, Deep Six. During his active membership as an Avenger, his hubris was an obstacle towards teamwork, and his rivalry with Hercules was particularly notable. His respect for his old comrade Captain America helped to keep this from becoming a major problem. The Defenders, with their looser organizational approach, allowed the Sub-Mariner the "space" he required. It was during his tenure with the Avengers that Namor helped recover the cocoon in which the Phoenix Force had placed Jean Grey, thought to be dead, years earlier. He also fought against Magneto when Magnus tried to rescue his students from Emma Frost, then White Queen of the Hellfire Club, and recovered his lost giant horn, which was found by the X-Terminators. Not long afterward, rogue elements of Atlantean society led by Attuma declared war on the surface, and Namor was presumed killed in the battle, though the Atlantean barbarians were defeated.
However, Namor had actually survived, and surfaced months later in the South Pacific. Nearly mad from his ordeal, he was found by Caleb and Carrie Alexander, a father-daughter team who quickly nursed Namor back to health. It was Caleb who revealed to Namor the truth about his blood chemistry and his "rages," and who equipped him with a monitor that warned him when he had to seek air or water. This allowed Namor to control his metabolism for the first time in his life. Determined to continue to preserve the oceans and his people, but without revealing himself, Namor raided sunken treasures to finance his purchase of an international company he renamed Oracle, Inc., using the Alexanders as proxy buyers. Shortly thereafter, however, Namor was forced to reveal his survival when a terrorist bomb detonated on an Oracle submarine super-tanker, threatening the lives of everyone in New York. Then, Namor lost his ankle wings when he unleashed a mutagenic scrambler inside the animated garbage dump called "Sluj" in order to stop the monster. He dealt with the world of high finance thereafter, though it brought him into conflict with the Super Skrull, and then to the dimension of K'un L'un, where he found the hero Iron Fist, who had been presumed dead for many months.
Returning to Earth and investigating the apparent invasion of Earth by the K'un L'un sentient plant race called the H'lythri, Namor was forced to fight Wolverine, who had been captured by the H'lythri and their associate Plant Man days before. The battle was fierce, but it was interrupted by the sorcerer Master Khan, who destroyed the plant people and returned Wolverine to his place. Khan then wiped Namor's memory and dumped him in the American Midwest, as punishment for interfering in his plans for Iron Fist. Namor was "missing" for almost a year, and was known as "Rex," until his cousin Namorita was able to track him down using a psychic link to him that she had recently discovered. However, Namor didn't recognize her and rejected her. He didn't regain his memory until a while afterwards, when he and the apparently-resurrected Princess Fen (his mother, who had saved him when he was thrown into the ocean by an explosion) were captured by Dr. Doom's new sonic ram fishing vessel. The boat itself was then magically imprisoned in a bottle by Master Khan, and Khan assumed Namor's form and sold off much of Oracle's holdings. Namor soon broke the bottle and the spell, and then ripped Khan's head off.
Immediately thereafter, Namor was called to Atlantis to deal with attacks by the ancient "Faceless Ones" on Atlantis's borders. Fen attempted to usurp the throne, and it was soon revealed that she was really the witch-queen Artys Gran, who had stolen Fen's body in order to release her husband Suma-Ket, a pagan sorcerer-king who had been banished by Namor's ancestor thousands of years earlier. Namor soon confronted Ket and was killed, impaled on Ket's spear. Fortunately, Father Neptune, the deity worshipped by Atlantis, appeared to resurrect Namor to fight Suma-Ket, whose religion threatened Neptune's existence. In the process, Namor's ankle wings were restored and he was given the sacred golden armor of his ancestor in which to fight. With the help of his people and comrades, Namor defeated Suma-Ket and his forces, though the real Fen, trapped in Artys Gran's body, died defending her son from a final attack from Socus, the villains' servant. Namor eventually returned to both ruling Atlantis and running Oracle, but has remained generally out of the surface world in recent days. Oracle, Inc. was also funding the charitable super-group Heroes for Hire, and the team used an Oracle facility as its headquarters.
Afterwards, Namor was involved in an international dispute with Wakanda and its King T'Challa (a.k.a. Black Panther), and had to deal with Attuma's uprisings again.
Most recently, a mystical curse from an old foe, the sorcerer Yandroth, bound Namor and the three other senior members of the Defenders--Doctor Strange, the Hulk and the Silver Surfer--to be transported to scenes of danger and trouble around the world, forcing them into the midst of one deadly crisis after another. Namor and his fellow Defenders eventually freed themselves from this curse, but not before they attempted to take over the world as "The Order," figuring that if they ran the world there would be no crises. The world's heroes tried to stop them, and eventually the curse was lifted. Namor has now allied himself with the new Invaders team, bringing the full might of his Atlantean army to bear wherever needed.
Namor was briefly reunited with his father with the help of Stingray, although the villainous Tiger Shark and Llyra later had Leonard killed.
Llyra also posed as the Invisible Woman to seduce Namor during a time when Mister Fantastic was believed dead. She gave birth to a son, Llyron, and aged him through forbidden magic and technology. Llyron confronted his father over the control of Atlantis, but he and his mother were eventually defeated.
When the Scarlet Witch altered reality in the event known as the House of M, Namor was idolized by the general public as the first super hero. He was also classified as a super human mutant (homo superior). However in M-Day, the event when 90% of the world's mutants were de-mutated or decimated, Namor retained his powers but was not included in the 198 Files. His supposed mutation has not been mentioned since.
It was revealed in the New Avengers: Illuminati Special that Namor was a part of the group, although he appeared to be very hostile and arrogant in his opinions and decisions of the Illuminati. Violently opposed to the group's decision to send the Hulk into outer-space exile, he left the group. His cousin Namorita was killed with the rest of the New Warriors in the Stamford explosion caused by the super-villain Nitro, which led to the Superhuman Registration Act. The Illuminati asked Namor back in this light, to consider the Act, but Namor opposed this as well. For vengeance of his cousin's death, Namor activated sleeper agents of the Atlantean Royal Guard to search for Nitro, who was instead found and captured by X-Man Wolverine. After Atlantean ambassadors sent by Namor are attacked, Atlantis begins rebuffing diplomatic overtures. Finally, in the climactic battle between the pro- and anti-registration heroes, Namor brings an army of Atlanteans to aid Captain America's forces.