Kull the Conqueror was created by Robert E Howard in a story called the Shadow Kingdom published in Weird Tales in August, 1929.
Born in the island nation of Atlantis, Kull was exiled for defending a condemned woman. As a wandering swordsman he gained many followers and eventually became king of Valusia.
Soon after becoming king he inadvertently frees a powerful supernatural being called The Skull of Silence. After repelling it from the world, he returns to Valusia where a Pictish emissary named Ka-Nu informs him that his court has been infiltrated by a sinister serpent-man cult. Together they defeat the serpent-men and lead a war party to destroy the serpent-men's temple.
At the sacking of the serpent-men's temple, Kull and Ka-Nu encounter Thulsa Doom another adversary of the serpent-men, and they bring him back to Valusia with them. However, Thulsa Doom is secretly plotting to gain supreme power by acquiring the Serpent's Eye gem from the temple, which is now in Kull's posession. He eventually tricks Kull into handing it over, which leads to a final conflict between Kull and Thulsa Doom before the entire Valusian Court. Kull triumphs when the power proves too much for Thulsa Doom to effectively wield.
Next Kull travels south with a fleet of ships to aid the island nation of Demascar in war with its neighbor Rikos. But one of his own lords, Kanuub, betrays Kull and helps Demascar use Kull's fleet as a sacrifice to summon demonic forces to aid them against Rikos. Kull eventually triumphs when Brule kills the sorcerer behind the spell.
After the return to Valusia, Kull learns that seven districts of the city have befouled water supplies. He leads two contingents of soldiers into the ancient city Qar, which lies below Valusia, where they encounter a giant monster. They slay the beast and the Valusian responsible for waking it.
Kull then becomes embroiled in a conflict with the Lake Men, due to advice he receives from Delcardes' talking cat. But he later learns that the whole thing was engineered by Thulsa Doom who 'passed to another sphere' but has returned to bedevil the king.
Sometime thereafter, Kull and two shiploads of Valusian warriors become shipwrecked on the island of the Leopard Cult where Kull must face a werewolf and a despotic ruler before they can sail home to Valusia.
It has been suggested that Kull may be an ancestor of Conan.