Dobtcheff

 was an alien stranded on Earth. He had scales on his body and pincers for hands, but disguised himself as a human.

Hundreds of years in Dan Blackwood's future, Dobtcheff and his people came to Earth to ask for help in defending their planet. Dobtcheff's ship was the only one to make it, and it was attacked by the humans. The ship was destroyed but Dobtcheff was sent back eight hundred years in time in a smaller craft. This ship was buried underground.

Dobtcheff took over a human baby's mind, and centuries later he gathered male descendants of the baby, including Dan, to use them to retrieve his ship. His possession of the men killed most of them, but Dan was more resistant to the control, and was rescued by the Second Doctor. Dobtcheff failed to retrieve his ship, not having enough men to control it. Dobtcheff was able to use Dan to set the ship's auto-destruct sequence, but the Doctor helped Dan reverse it. Dobtcheff, having reverted to his natural form, died. (PROSE: Reunion)