Triton was a moon that orbited the planet Neptune, the eighth planet of the sol system. It was originally a rogue planet until it was caught in Neptune's orbit.
Triton was a cold moon with a thin nitrogen atmosphere. It had frozen pink poles, volcanoes of ice and solid lakes. It was inhabited by the Waro. (PROSE: The Devil Goblins from Neptune)
By the 38th century, Triton was inhabited by humans. Their society showed a belief of multiple deities, and bred grunts. At some point, Gagan Rassmussen revolutionised Triton with his invention of Morpheus sleep pods by minimising the human need for sleep and allowing them to be far more productive. However, Rassmussen's attempts to make the pods more powerful tampered with the human brain chemistry to remove the need for rest, but the chemistry which regulated the production of sleep dust in people's eyes was also altered, causing the sleep dust to mutate and coalesce into the Sandmen, carnivores that fed on humans.
The Twelfth Doctor and Clara Oswald sought to eliminate every last Morpheus pod on Triton after seeing the carnage the Sandmen wrought at Le Verrier space station. However, Rassmussen had mutated into one of the Sandmen, who was sentient and intelligent enough to initiate a plan to infest the solar system with more of his kind. (TV: Sleep No More)
The space pirate Baltazar was referred to as the "Corsair — King of Triton in the 40th century". (TV: The Infinite Quest)