Stigorax

The Stigorax was a species native to Terra Alpha. The Seventh Doctor described them as 'ruthless, intelligent predators.' By the time of the rule of Helen A, there was only one left.

Biology
The Stigorax were rat-like carnivores. They fed on humans and were feared by the Pipe People of Terra Alpha. Despite this, they could be tamed. (TV: The Happiness Patrol)

History
The Stigorax were native to Terra Alpha. They hunted the Pipe People. When the humans came to Terra Alpha, they were almost wiped out, apart from one named Fifi. Fifi was tamed by Helen A, leader of the Happiness Patrol. Fifi obeyed Helen A's commands and was sent to hunt people who opposed her. Fifi was killed while trying to hunt down the Seventh Doctor, rendering the Stigorax species extinct.

Before this, the last time the Doctor encountered a Stigorax was in Birmingham in the 25th century. (TV: The Happiness Patrol)