Caxtarid

The Caxtarids were a humanoid species with metallic red eyes and hair. (PROSE: Infinite Requiem) They had dense muscles and strong honeycomb bones. (PROSE: Wringing Off)

They were experts in creating living torture machines, such as the Prompter of Confessions and the Manacle of Flesh. Preserved human eyes were considered to be trophies of high value in their culture. (PROSE: Infinite Requiem)

History
Caxtarids were native to Lalande 21185 in the constellation of Ursa Major. (PROSE: Return of the Living Dad)

The Caxtarids invaded Kapteyn 5 and enslaved the Kapteynians, exterminating four of the indigenous sentient species. (PROSE: The Room With No Doors) Some Caxtarids lived on Ha'olam. (PROSE: Seeing I)

Two Caxtarids, Roze and Indigo, interrogated the Doctor on 11 December 1983. They were later discovered dead in a morgue, apparently killed by Ellen Woodworth. (PROSE: Return of the Living Dad)

The Doctor attempted to prevent a plague from wiping out the Caxtarid species (and everything else on their world with DNA) eight Lalandan years prior to Earth year 1983. The "democratic" Lalandan government had created a virus as a defence against a brewing rebellion, but the Doctor stole it. Without the government's threat of the virus, a rebellion erupted and many Caxtarids died. Roze and Indigo only barely escaped. Two Lalandan years after 1983, another rebellion provoked the Lalandan government into deploying a viral cache; the virus escaped into the wild and killed every living thing on the planet within five years. It even chewed up the hulls of the ships the Caxtarids would have used to escape. The Doctor returned, but it was too late. "History had already locked in place." (PROSE: Return of the Living Dad)

In the 30th century, Sokolovsky's albino appearance terrified a Caxtarid mercenary so badly that he got the drop on her. (PROSE: So Vile a Sin)

Fitz Kreiner once held a rock concert (with six other musicians) to break the Caxtarids' mind control on Telemahuka. (PROSE: The Year of Intelligent Tigers)

Two Caxtarid slavers operated the prison transport carrying Pyke-Xi Raul to the Sixth Homeworld. When it crashed on Bokuvell, one of the Caxtarids died; Pyke killed the other with a rock. (PROSE: Wringing Off)