ALTERNATE VERSIONS - Page 2
In What If? (1st series) #41, Namor defeated Destiny before the villain could destroy Atlantis or render its royal prince an amnesiac. As Namor was disposing of the Helmet of Power, however, Byrrah took advantage of the situation to manipulate an injured King Thakorr into "temporarily" giving Byrrah the signet ring that named Byrrah acting emperor until Thakorr recovered. Once seated on the Coral Throne, Byrrah arranged for allies like Krang and Kormak to help him turn the people against Namor before the prince returned. He then murdered Thakorr in his sleep and planted the bloody dagger in Namor's room. An infuriated Namor fled from Atlantis, his good name besmerched.
In exile, Namor was approached by Lord Neptune himself, who foresaw great strife for Atlantis and offered Namor his sacred Trident as a rallying symbol to reclaim the faith of the Atlanteans. Proud Namor rejected his god's offer, however, refusing to beg the fickle Atlanteans to take him back. In Namor's absence, Byrrah's rule produced a weakened state, and Atlantis was attacked by Attuma's barbarians. Members of the royal guard fled to find Namor and seek his aid in defending Atlantis, but again Namor refused to aid his people. Only when a second guardship arrived with word of his mother's death did Namor return, seizing the Trident of Neptune and slaying Attuma in single combat for his crimes.
And yet, the Atlantean people had no thanks for Namor. Their spirits had been broken under the tyranny of Byrrah and the slavery of Attuma. Knowing Namor could have aided them earlier but chose not to, the Atlanteans went into self-exile, scattering into the waves never to return to Atlantis and their lonely prince on the throne.
In What If? (2nd series) #28-29, Steve Rogers saved Abraham Erskine from a Nazi assassin's bullet, allowing the Super-Soldier Program to continue after him. A battalion of super-soldiers were deployed into Europe shortly after Pearl Harbor, bringing a quick and definitive end to World War II. 
As a result, Namor never entered the war and the Invaders were never formed. Namor still fell into his amnesiac state after encountering Destiny, but in the years that followed Steve Rogers revealed his identity and became President, forging the United States into a fascist Super-Soldier state. Namor regained his memories while being hunted by S.H.I.E.L.D., only to have a fateful encounter with a tribe worshipping a man encased in ice up north. This man was revealed to be the true Steve Rogers, and his imposter was the Red Skull in Rogers' body. Namor joined Captain America and several others in forming the Avengers to overcome this villainy.
As a resident of Utopia when Legion's 'X' personality began acting up, Namor was swept into the Age of X pocket reality. Like all the mutants there, he spent 1000 days defending Fortress X and the last survivors of mutantkind from a relentless onslaught of human military forces.
Namor and Ororo found love with one another over the course of the siege, forging bonds as the prince and the goddess. When the Age of X ended, both chose to have their memories of that other life erased by Emma Frost and the Cuckoos, to preserve good relations between Atlantis and Wakanda, whose king Storm was married to at the time.
In the House of M, Namor was ruler of the kingdom of Atlantis, one of several semi-independent nations allowed to exist by Magneto while his consolidated control over America.
The version of this Namor who existed on Battleworld found the situation untenable, and conspired with Prince Pietro to overthrow Magneto. The usurpers claimed the throne but not Magneto's head, as the king went underground with the help of Polaris and some unlikely human allies. Namor turned against Pietro in the hopes of claiming all the lands and seas for himself, but Magneto returned and turned Namor's own trident into metal shrapnel, ripping the Atlantean to shreds for his betrayal.
In the series Namor: The First Mutant, a crossroads came where Namor and his lover Abira had to chose whether to activate her mystical potential as a Logomancer, 
which would remove her ability to love another. In the original timeline, they refused, and a catastrophe that a Logomancer could have prevented led to the destruction of both New Atlantis and the mutant colony of Utopia. Namor and Abira's son grew up in an increasingly hostile world brought to the brink of war. He ultimately came to blame his parents for their failures of duty, and forged an alliance with Doctor Doom to transport backwards in time. The son of Namor and Abira intervened at the crossroads and convinced his mother to accepted her Logomancer destiny. New Atlantis was saved, but Abira's love for Namor was gone, and so their son and his future ceased to exist.
Sub-Mariner: The Depths presented an odd story for the Marvel Knights imprint, a steampunk inspired tale of explorers looking for the lost city of Atlantis. Doctor Randolph Stein, a professional scientist and "debunker" of myths and legends like Sasquatch, is hired to crew a submarine. He is tasked to follow up on a previous mission to find Atlantis. In the depths, the crew tell tales of the mythical Namor who has been spotted by God-fearing mariners. Stein dismisses the tales, until he has an encounter himself. Told entirely from the perspective of the explorers, Namor's true origins and motivations are deliberately left a mystery in this world.
Namor Miyamoto was the son of Great Atlantis and sworn protector of Imperial Japan. He failed in his duty when the Atlanteans flooded the surface world, 
killing millions of innocents including the people of Japan. Namor went to Atlantis for justice, only to see the other half of his people eradicated by a fascist version of Charles Xavier in retribution for the surface attack. Denied his vengeance and having failed to protect his two nations, Namor spent a decades hunting Xavier and his surviving colony of Aryans. Crossing paths with Dazzler and her team of cross-dimensional X-Men, Namor finally had his revenge. This victory still left him hollow, however, for his people were still dead despite all his efforts.
On Earth-001, dubbed Loomworld by its rulers the Inheritors, Namor was pirate king and scourge of the seven seas instead of a water-breathing Atlantean. 
He had a relationship with Lady Jessica Drew, one of the highborn servants of the Inheritors, for first pick of any jewels or finery he seized. Spider-Woman, the Jessica Drew of Earth-616, manipulated Namor into disposing of her doppelganger for a time by sealing her in a trunk and taking her out to sea. After Spider-Man, Spider-Woman, and the Web Warriors overthrew the Inheritors, Jessica-001 and Namor returned to harbor and were positioned to take over and restore order in the rioting that followed.
In Marvel 1602, the Age of Marvels began some four hundred years early. The Four from the Fantastick and their nemesis, Otto von Doom, went sailing for the edge of the world and discovered Numenor, Emperor of Bensaylum. 
The Lord Mariner could fly with his winged sandals and used the Trident of Poseidon to control water itself. His island nation welcomed the visitors with open arms once he spotted Susan Storm. Numenor and von Doom plotted to eliminate Richard Reed and Benjamin Grimm so Numenor could claim Sue for himself. However, Doom and his allies the Four who are Frightful also sought to steal the magic of Numenor's trident. In the process, they shed the blood of Numenor with his own trident, fulfilling a prophecy that Bensaylum would disappear beneath the waves should such a fate ever take place.
On Earth-691, the reality of the 31st century Guardians of the Galaxy, the early 21st century saw what became known as "The Great Injustice". 
Ever-increasing anti-mutant sentiment led to powerful Sentinels being unleashed on the mutant population. Magneto gathered the surviving mutants of Earth in a great exodus to the stars, leaving mankind behind. It was Namor who remained behind, guarding their escape, and seemingly gave his life to destroy these Sentinels once and for all.
In the future of Captain Marvel: The End, Earth was brought to a dystopic end by the events of the First and Second Last War. Although Namor fought alongside the heroes in the first war, he 
chose to retreat beneath the waves afterwards and fortify Atlantis, leaving the surface-dwellers to their fate. Namor was joined by Amora the Enchantress, the Asgardian goddess who became his queen, and later the mother of his son, Prince Ove. The prince proved to be viciously selfish, though, and lashed out at his father as a teenager in order to seize power. Namor chose not to fight back and died at the end of Neptune’s Trident.
In Future Imperfect, King Namor ruled over the underseas cities which continued to thrive after humanity destroyed themselves with nuclear weapons on the surface world. He had a queen, Nuuma, and a son, Prince Leonard. Eventually, the Hulk resurfaced and became Maestro of Dystopia, leading Namor to fear humanity would rise again. Working with the android Human Torch and the Abomination, Namor tried to kill the Maestro, but failed. Maestro retaliated by attacking Namor's Pacifica kingdom, and his wife and son died in the assault. In his grief, Namor attacked Dystopia with Giganto, but once again failed to defeat the Hulk. Allied with Doctor Doom, he apparently died when the Torch's nova flame was activated, obliterating their castle in Latveria.
In Sins of Sinister, Mister Sinister finally succeeded in corrupting the Krakoan resurrection process, ensuring that each individual resurrected was tainted by his genes and ideals. After suborning the Quiet Council, they quickly began killing and resurrecting key mutants. Namor had already been killed and turned by the Sinister Emma Frost before Doctor Doom approached him for an alliance against Krakoa. The Sinister Namor killed Doom and installed a meat puppet on the throne of Latveria, wholly controlled by the Council. Namor soon occupied an empty seat on the Quiet Council once Storm, Mystique and Destiny left to preserve their independence. After 1000 years, the Sinister mutant race had conquered the galaxy. Namor was Imperator of the Drowned Worlds, sire of the Knight Consorts who worked in alliance with Emma, Empress of the Red Diamond.
In Namor: Conquered Shores, decades passed and the threat of global warming finally consumed the Earth, with the help of the alien Kree. Most of Earth’s heroes were lost pursuing the Kree into space for a counterstrike. Atlantis was now the only true power left on Earth. Some humans still tried to live on what remained of the surface, while others resided in an air-filled reservation within Atlantis. Because of the damaged environment or other variables, though, surface men could no longer successfully procreate, and the air-breathers were slowly dying out. Namor had abdicated the throne to Namorita, serving only as an occasional intermediary with Steve Rogers in Atlantis and Luke Cage on the surface. A new war almost broke out over a machine colony led by the original Human Torch, but Namor managed to control his rage and chose to follow the path of peace.