Hydroflax

King Hydroflax was a merciless conqueror and pillager whose subjects included the people of Mendorax Dellora and the Shoal of the Winter Harmony. He was infamous as "the Butcher of the Bone Meadows", who ate his enemies after battle, alive or dead. He consisted of a cybernetic head and a massive robot body with an autonomous computer.

In 5343, Hydroflax led a raid on the Halassi Vaults. The Vaults exploded in the ensuing firefight, driving the Halassi Androvar into his skull. River Song, who had been tasked by the Halassi to retrieve the diamond, posed as Hydroflax's nurse and seduced him into marrying her. Days later, she crashed his flying saucer into Mendorax Dellora, knowing she would intersect the Doctor's timestream there.

Hydroflax eventually discovers that River hired a surgeon to remove his head to get at the diamond and orders her killed, removing his head to prove a point. After the Doctor threatens his head, his robot body stops and Ramone teleports them away. Chased by Hydroflax's body, River takes them to the Harmony and Redemption to sell the diamond, but discovers that the passengers all follow Hydroflax. Hydroflax is reunited with his body, but a scan determines that his cellular structure has degraded too much and the diamond continues to move around inside his head, meaning he will be dead in seven minutes. After Hydroflax orders his body to do whatever it takes for him to survive, the body blasts his head to ashes, intending to take the Doctor's to replace Hydroflax. The Doctor eventually manages to destroy the robot's computer by connecting it to all the banks in the galaxy, causing the computer to be "deleted in a merger."

Hydroflax's robot body is eventually recovered on Darillium where the heads of Nardole and Ramone share control of it and work in a restaurant in front of the Singing Towers. (TV: The Husbands of River Song)

Hydroflax