From TARDIS Index File, the free Doctor Who reference.

Stigorax
Place of origin:	Terra Alpha
Appearances:	DW: The Happiness Patrol
Notable Individuals:	Fifi

The Stigorax was a species native to Terra Alpha. By the time of the rule of Helen A, there was only one left.

Biology

The Stigorax was a rat-like carnivore. They fed off Humans and were feared by the Pipe People of Terra Alpha. Despite this, they were tameable. (DW: The Happiness Patrol)

Helen A and Fifi, a Stigorax. (DW: The Happiness Patrol)

History

The Stigorax were a native species on Terra Alpha who hunted the Pipe People. When the Humans came to Terra Alpha, they were almost wiped out, apart from one of them named Fifi. Fifi was tamed by Helen A, leader of the Happiness Patrol. Fifi obeyed the commands of Helen A and was sent to hunt people who opposed her. Fifi was killed when trying to hunt down the Doctor. (DW: The Happiness Patrol) Therefor Fifi was the last of her kind.