Xaltotun is the main villain of the Conan the Barbarian's story ''The Hour of the Dargon'' by Robert E. Howard and its comic book adaptations by Marvel and Dark Horse.
He was the ruler of Acheron, an ancient dark empire of wizards who worshipped the snake god Set.
In the story he's ressurected by a Group of conspirators who wanted a powerful ally to help them overthrow Conan, the king of Aquilonia. These conspirators were Orastes, Tarascus, Amalric and Valerius.
However, Xaltotun cared very little for their ambitions and he plans to recreate the empire of Acheron with a massive blood sacrifice.
He's eventually defeated by Conan and his companions by using an artifact called the Heart of Ahriman.