Coloth

Coloth was a young Ulk-Ra who was brought back to life by the Plume Coteries to act as an agent of theirs. (PROSE: White Canvas)

Original life
Coloth grew up on a planet home to his people, the Ulk-Ra. He had a brother 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-male brutally killed Coloth by slicing him open with his paws. (PROSE: War Crimes)

Resurrected by the Plume Coteries
In "a long story that could be a book in itself", Coloth was brought back to life by the posthuman Plume Coteries and given the ability to shapeshift. (PROSE: White Canvas) In his new life, Coloth sometimes gravitated to being a cactus-skinned humanoid. (PROSE: Cobweb and Ivory, White Canvas, 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 once spent some time working at the Plume Coteries' library alongside Marissa. He greeted Graelyn Scythes, Archimedes von Ahnerabe, and Lady Aesculapius when they came to the library with Auteur and helped them find The Book of the Enemy. After they used the book to determine the Original Mammoths were responsible for the attacks on the 10,000 Dawns, Coloth, motivated by the concept of Ulk-Ra bravery, offered to come with them to the Mammoths' home. Along with almost everyone else in the Mammoth's domain, Coloth was turned to fiction when Auteur revealed her masterplan and nearly completed her ritual circle. Coloth had a movie series in Auteur's Town which included Coloth Adventures 4: The Patron of Doom. Coloth escaped from fictionality during the Town's destruction and briefly fought the Firmament with Lady Aesc. Later, he was present at the Needle during the signing of the Christmas Needle Agreement, playing cards with Archimedes, Aesc, and many other aliens. (PROSE: White Canvas)

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."