Tsotha-lanti is a Kothian wizard, having a reputation for cruelty that's used by parents to scare their children as well as masters, threatening to sell their slaves to him. He has no respect for human life, flaying live humans to use their skin as parchment. His home is the Scarlet Citadel, where he performs his cruel experiments. In the dungeons below the citadel he has many dark creatures, such as his enormous snake Satha.
Tsotha-lanti, together with Strabonus, king of Koth, and Amalrus, king of Ophir managed to trick Conan into comming to Koth to help Strabonus against the invading forces of Ophir. When Conan came, he found that Amalrus was indeed not attacking Koth, but that they had tricked him to comming there in order to trap him. Being outnumbered, the Aquilonian knights Conan brought didn't flee, but attacked the hosts head on, killing many of their soldiers, but in the end was crushed by sheer numbers. The soldiers was unable to capture Conan himself, who slayed anybody who came within sword's reach. At last, Tsotha-lanti desided to intervene and was able to sting Conan with a small spike laminated with the juice of the purple lotus, paralyzing Conan.
They took Conan to the Scarlet Citadel and offered him money and freedom if he signed over his kingdom to Price Arpello of Pellia. Conan refused, and was thrown into the Halls of Horror deep below the citadel.
The forces of Ophir and Koth then went to siege the city of Shamar, but Conan managed to escape from the Halls and return to Tamar through the help of Pelias. Conan gathered an army and went to meet the invaders. Surprise by the return of Conan, and by the sudden apperance of another enemy army, the invaders were slaughtered. Tsotha fled from the battle, but was pursued by Conan. Then, a eagle came down from the sky towards Tsotha. It scared his steed, so that it threw it's rider off, and Tsotha and Conan was left to battle. Conan managed to decapitate Tsotha, but as the head fell to the ground, the body did not stop moving. Tsotha was still alive, his body searching for his head. Then came the eagle down from the sky again, picking up the severed head of Tsotha and flying away, laughing with the voice of Pelias. Tsotha's headless body ran after the eagle and disappeared.