Namor MacKenzie, the son of human Leonard MacKenzie and Atlantean Fen, became the superhuman Sub-Mariner in the early 20th Century. Fen died in a bombing on Atlantis, and Leonard, who was believed dead, eventually remarried and fathered another son, Lawrence, who in turn fathered Leon. Leonard was eventually killed, while Leon was employed by the rich Marrs Corporation. Meanwhile, Namor developed a long-standing rivalry with the metamorph Llyra, the former empress of another undersea kingdom, Lemuria. Llyra desired to wed Namor to claim Atlantis' throne, but Namor developed a deep hatred of her, partly because she caused the death of Namor's actual bride, Dorma. In an elaborate plot, Llyra posed as Phoebe Marrs, the owner of Marrs Corporation, and seduced Leon MacKenzie, intentionally becoming pregnant. To conceal her true plans,she posed as Namor's old flame Invisible Woman (Sue Richards) and seduced Namor so that he would believe her child to be his, though as a hybrid Namor was infertile.
Llyra then found the cave of Vyrra, an Atlantean scientist exiled for his illegal cloning experiments, one of which cloned Namor's cousin, Namora, producing a cloned child whom Namora raised as Namorita. Vyrra genetically accelerated Llyra's child's birth and aging. Not wanting the child to be mindless, Vyrra copied Llyra's mind and memories into its brain, but secretly copied his own mind into the brain as well, wanting part of himself to live on in a powerful form. These two minds, merging with the child's own slowly developing mind, produced a brilliant and deadly composite psyche with full access to Llyra's memories and cunning and Vyrra's vast scientific knowledge and ambitions. When the male child awoke, he was genetically developed to age 16, and proved to be a super-powerful amphibian like Namor, though Llyron's skin was green like his mother's. Llyra murdered Vyrra, unwilling to share her secret with anyone else and unaware that Vyrra's mind had been copied into Llyron's as well, then named the child Llyron (likely after her father), and took Llyron to undersea Atlantis. She announced that Llyrcn was the son of Namor and thus had claim to the throne. Despite Namor's protestations, Llyron won the loyalties of Atlantis' ruling council by defeating Namor's allies, the criminal Tiger Shark and his lover Tamara Rahn.
Seeking to further discredit Namor, Llyron, as ambassador to Atlantis, approached the United Nations with an offer of alliance, which the UN. later accepted. Llyron successfully repelled a pre-arranged attack of sea monster assault — including the walking whale Giganto (offspring of its namesake who had died in battle with the Fantastic Four years before) and the parasitic Hagfish, which Llyron slew — framing Namor with attacking the surface world with these monsters as heralds. Llyron was soon hailed as Atlantis' ruler despite his true parentage being revealed, as Atlantean law recognized Llyron and Namor sharing a common ancestry and willingly declared Llyron rightful ruler. Llyron had Llyra imprisoned, at which point she realized that Vyrra's mind inhabited Llyron's form as well; Llyron later constructed a monument to Vyrra on Atlantean soil. When the sorceress Morgan Le Fay raised Atlantis to the surface, much of Atlantis' population was killed, and Llyron used his leadership skills to gather the people together. Llyron ordered that all the fertile women of Atlantis be implanted with clone fetuses so that a powerful army could be raised with which to attack the surface world, a likely plot of Vyrra's. It is unknown what became of this plot or why Llyron was removed from power, but Atlantis soon elected a new ruler.