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. Holding a gun to Nardole's head, the body forces him to draw in Ramone whose head the body takes while storing Nardole's within itself.

On the Harmony and Redemption, the body pulls Nardole's head out of storage to confirm River's identity before putting it back against his protests.

After the crash of the Harmony and Redemption on Darillium, Hydroflax's body is recovered from the wreckage. As the hostile onboard computer was destroyed by the Doctor, Nardole and Ramone share control of the body, working in a restaurant situated before the Singing Towers. When River arrives several years after the crash, Ramone is in control as Nardole is getting some "me time" inside the body, something he admits is hard when he greets River from inside Hydroflax's body. (TV: The Husbands of River Song)