Rat King

A  was the leader of some sentient rats, living in Cadogan Tunnels. It was created when a set of rats interlinked tails, allowing the rest of the rats to speak. It made humans do the activities. The humans used to experiment on them. It was killed by its creator Dr Christopher Wallace by its own punishment fluid. (AUDIO: Rat Trap)

The Seventh Doctor and Ace encountered a Rat King on the planet Epajaenda Resource Sphere. (PROSE: Last Rites)