The origins of Suma-Ket and the Unforgiven Dead remain a mystery. They worship the race of extradimensional demonic Old Ones; Ket's race has also been called Old Ones. Ket is a necromancer and possibly a demon, the stuff of dark legends come to life. Circa 5800 BC, Ket led the Unforgiven Dead southward to the mid-Atlantic city Atlantis, which was beset by the monstrous Faceless Ones. In exchange for his people settling in Atlantis, Ket magically banished the Faceless Ones. In awe of Ket's battle prowess and mystical powers, the Atlanteans slew their king Harran, the son of Atlantis founder Kamuu, and proclaimed Ket Atlantis' king. The seemingly messianic Suma-Ket proved a demonic tyrant, bringing a new religion of deities both foul and fell. Via infant sacrifice and other atrocities, much Atlantean blood fueled his forbidden magics. Ket's vicious Nereid servants delivered his foes to him. Atlanteans initially worshipped Suma-Ket, fearing his wrath: but as their children fell in the name of his abominable religion, their prayers turned to cries of vengeance. Kalen, grandson of Kamuu and wearer of the sacred armor of Atlantis, returned after a long journey and rallied Atlantis. Aided by their patron god Neptune, the Atlanteans defeated Ket's forces in a bloody battle that turned the oceans indigo, but the Unforgiven Dead could not be destroyed. The lords of Atlantis banished Ket's court beyond the Earthly plane to the Grey Waters, a mystical prison not quite death, but certainly not life. Artys-Gran, Ket's wife and last of the Unforgiven Dead, was slain and her body hidden, breaking Suma-Ket's covenant with his dark gods; Ket prophesied that he would return when the blood of his people possessed the blood of Kalen.
In 1958 AD, Ket's agent, the halfling Socus, located the dying princess Fen (mother of Namor the Sub-Mariner) amongst the ruins of Antarctic Atlantis (destroyed by Paul Destine). Socus somehow transferred Artys-Gran's spirit into Fen's body, and Fen's spirit into Gran's body; this initiated the first part of Ket's prophecy. Fen's true body was magically rejuvenated, and in recent years she returned mysteriously and gained Atlantis' throne. Socus subsequently sacrificed the Atlantean prince Byrrah, whose royal blood opened the doors imprisoning the Unforgiven Dead. Ket sent the Faceless Ones on a carnivorous stampede across the ocean floor, he eventually battled Namor, shoving his magical blade through Namor's torso, left to die, Namor was revived by Neptune, who granted him Kalen's sacred armor. Learning the secret of "Fen," Namor recovered the real Fen (in Gran's body). Meanwhile, the death of the Atlantean Dara—who recognized Gran's treachery and tried to restrain her — at the hands of an unwitting guard served as the sacrifice to allow the Unforgiven Dead to storm Atlantis. The true Fen used Gran's body's magic to transport herself, Namor and his allies (Tamara Rahn, Seth, Morel, Tiger Shark) back to Atlantis. The true Fen helped rally the Atlanteans to fight their attackers, and soon the Gran-possessed Fen was slain, and Namor used the sacred Trident of Neptune to slay Ket after a savage battle. Without Ket's magic, the Unforgiven Dead became simply dead, their inert corpses were consumed by the ravenous Faceless Ones. Socus, however, slew the true Fen (in Gran's body) before escaping.