Thulsa Doom is the prototype for many of the future undead evil wizards in Howard's stories, such as Tsotha-Lanti (in the Conan saga) and Kathulos (in the Skull Face novelette); other living or revenant Howardian practitioners of magic such as Thoth Amon, Thugra Khotan, Kathulos, and Xaltotun bear some psychological similarities to Thulsa Doom even if their actual appearance is vastly different.

Howard later edited the text to include foreshadowing/references to Thulsa Doom (as he had been renamed) throughout the story and changed the title to The Cat and the Skull to reflect this.

He is seemingly invulnerable, boasting after being trampled by one of Kull's comrades that he feels "only a slight coldness" when being injured and will only "pass to some other sphere when [his] time comes".

Thulsa Doom returns in Kull the Conqueror #11, "By This Axe I Rule", based on an original story by Robert E. Howard.

Posing as the nobleman Ardyon, he forms an alliance with four rebels within Valusia: the dwarfish Ducalon, the soldier Enaros, Baron Kanuub, and the minstrel Ridondo, who actually dethroned the hero, and set him on a quest to regain his lost kingdom, in the pages of his own comic, until it was cancelled.

Thulsa Doom allowed Norra's age to catch up with her, turning her into a shriveled corpse, and then revealed himself to Kull, challenging him to one final battle.

The script for that issue was an adaptation of the prose tale "Riders beyond the Sunrise", itself the completion by writer Lin Carter of an untitled fragment written by R. E. Howard.

American company Dynamite Entertainment published a Thulsa Doom mini-series written by Arvid Nelson, with art by Lui Antonio, for a total of four issues in 2009.

[10] Thulsa Doom later becomes an enemy of the Celtic hero Cormac Mac Art, another Howard character further expanded by Andrew J. Offutt.

As depicted by Offutt, Thulsa Doom possess remarkable shape-changing powers, being able to take not only the form but also the precise mannerisms of Cormac mac Art's close friends.

Pre-production drawings showed this version of Thulsa Doom with the skull-like face, but as filmed, he is essentially the classic Conan villain Thoth-Amon, servant of the serpent-god Set.