Coloth

Coloth was a young Ulk-Ra.

As an Ulk-Ra
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)

As a cactus-skinned boy
Coloth was later resurrected, remembering that "[his] family, friends, and homeplanet [were] perfectly fine, but [he had] died a horrible death". He claimed that this was a "long story". (PROSE: Sonnenblumen) He became a member of the Plume Coteries, becoming friends with his birdhemoth steed Rich. (PROSE: Sonnenblumen)

In his new life, Coloth had the ability to appear however he wished, being known to adopt such forms as "a young man who looked exactly like Harry Styles from the band One Direction" or "a massive writing ball of tentacles". His most favoured appearance, however, resembled a cactus-skinned humanoid (PROSE: Cobweb and Ivory, A Farewell to Arms) with yellowish-green "skin". He could manipulate the details of this appearance at will, for example growing flowers on his skin. (PROSE: Sonnenblumen) Aesculapius was aware that he was an Ulk-Ra but also a "shape-shiter". (PROSE: Life After Death)

In his new body, Coloth, a "cactus-skinned boy", 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)

As part of his duties with the Coteries, he was present in the Plume Coteries' Library when it was visited by Graelyn Scythes, Archimedes Von Ahnerabe and Lady Aesculapius, of the 10,000 Dawns, who were looking for a copy of The Book of the Enemy alongside a person claiming to be an agent of the mammoths' opponent in the War, "the Emissary", but who was really solo operator Auteur. Coloth got Marissa to give him a glowing library card which would lead the travellers to the Book. After they found it and discovered that their next destination would need to be the mammoths' stronghold, Coloth, stating that "an Ulk-Ra lives on bravery", abruptly volunteered to go with them, since his library shift ended in five minutes anyway.

Subsequently, he was turned into fiction by Auteur using the gauntlet, and existed as such within Auteur's Town as a series of Coloth Adventures films for 17 years. One of them, which came out when Graelyn (who'd been reverted into a baby) was ten, was Coloth Adventures 4: The Patron of Doom. Eventually, Graelyn remembered her original life and freed all the fictionalised characters from the town's cinema. In the following battle between the defictionalised prisoners and the inhabitants of the Town, Coloth was seen fighting a group of cultists who were members of Auteur's people, back-to-back with Lady Aesculapius. They were all very briefly fictionalised again when Auteur manipulated Graelyn into completing her original ritual, but this didn't last as Graelyn outwitted Auteur and used the gauntlet to reverse all the fictionalisations and send everything Auteur had gathered back to its proper reality. The next day, Coloth attended the Christmas Needle Agreement negotiations on the Needle, and, after the document was signed, played a card game with Lady Aesc, Arch, and a great number of aliens; at one point, he won a hand against an alien with a tentacled face, to Aesc's amusement. (PROSE: White Canvas)

Still a "cactus-skinned boy", Coloth once flew beyond his native universe on Rich's back. As they were passing through the 10,000 Dawns, Rich's wingbeat caused a "rogue wave of dimensional pressure" which led to a Galaxy Accident befalling the Sun of the beings of light's Dawn. Realising the subsequent plague of Invisible Infernos was somehow their fault, the two stayed in the Dawns, helping Dawn to deal with this crisis as well as others, including the destruction of Dawn 10000. (PROSE: Sonnenblumen)

As a cactus-skinned man
Now a cactus "man" rather than a 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)

The adult Coloth was one of the individuals who showed up to Aesculapius's funeral in her Factory of Crystal, secretly a ploy by Aesc (who'd been reborn in a new body) to find out who had sent the trapped parcel which had taken her previous life from her. Coloth nearly bumped into a highly ominous man with a black goatee, dressed in all black with crimson robes, whose every word seemed to be a double entendre implying that he was the one who'd killed Aesc; however, it later became clear the goatee-sporting man was an old friend of Aesc's called Steve whom she seemed to trust completely despite his villainous stylings. Aesc deduced that her killer was instead an old acquaintance in a new body; she specified that even though she was looking for a shape-shifter, she did not suspect Coloth, who was relieved to hear it. Instead, the culprit turned out to be Meistras. (PROSE: Life After Death)

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."