Coloth

Coloth was a young Ulk-Ra.

Original life
Coloth grew up on a planet home to his people, the Ulk-Ra. He had an older sister named Otchon, who once let Coloth taste reed wine.

Tasked by the chief male of his clan, a young Coloth underwent a rite to become considered a warrior: he went out into the wild with the goal of killing a beast and bringing back its pelt. However, Coloth was captured by Ossu-male, an Ulk-Ra augmented by the War Lords for the War Games and returned to Coloth's homeworld by the Time Lord High Council. Coloth was kept trapped in woven vegetation for a period until — on orders from the War Lord programming — Ossu brutally killed Coloth by slicing him open with his paws. (PROSE: War Crimes)

Resurrected by the Plume Coteries
In his new life, Coloth sometimes gravitated to being a cactus-skinned humanoid. (PROSE: Cobweb and Ivory, A Farewell to Arms)

Coloth represented the Plume Coteries on Terra Primagenia at the unveiling of Cernunnos. Fleeing from a painted warrior during a praxis trip, Avus shoved past Coloth and was hurt by his cactus skin. (PROSE: Cobweb and Ivory)

Coloth and his birdhemoth friend Rich once visited the 10,000 Dawns. As they attempted to return home, Rich's wingbeat accidentally sparked a chain of events resulting in dangerous physical phenomena, Invisible Infernos, proliferating throughout the Dawns; the duo stayed behind until they could eradicate them. (PROSE: Sonnenblumen)

As a cactus man instead of a cactus boy, Coloth once walked through a section of the Labyrinth resembling a regular alley. Nezf, Wade, Tabrenilsodvoravitas, and a Shift passed Coloth on their way to steal the Greater Key from the Fortress. (PROSE: A Farewell to Arms)

Behind the scenes

 * Prior to Coloth's cameo appearance in Nate Bumber's Cobweb and Ivory almost 20 years after his debut in War Crimes, Bumber contributed a story foreshadowing Coloth's reappearance, titled The Library At the End Of the Universe: A Comprehensive History, to the 2017 fan anthology Shit Trips 2. The story features the Thirteenth Doctor and a boy named "Callum" in the Plume Coteries' library preparing for Coloth's arrival, with the Doctor at one point saying, "History has been broken. The most important person in all of time and space was killed before their time, and they'll be coming through here any day."