Nardole

Nardole was a member of the human colony of Mendorax Dellora, and an employee of River Song.

He was told to find the surgeon Professor Song needs to extract the Halassi Androvar from the head of King Hydroflax. Unfortunately, Nardole finds the Twelfth Doctor and brings him to Professor Song instead.

When River and the Doctor escape Hydroflax’s ship with his head in a bag, Hydroflax’s mechanical body turns to Nardole for strategic information. Although Nardole claims to know little of River’s plans, there is only one way for Hydroflax’s body to be sure, so it removes Nardole’s head and attaches it to its own! Now Nardole is forced into pursuit of the Doctor and Professor Song.

After the crash of the starliner on Darillium, Hydroflax’s body is rescued from the wreckage and Nardole is able to survive inside. (TV: The Husbands of River Song)