Lee Clayton

Lee Clayton was a companion of the Doctor. While the Judoon's scans identified him as human, the Thirteenth Doctor later assumed he had a bio-shield. He had received identical training to that of the Gallifreyan Gat.

He accompanied the Doctor while she hid on Earth in the early 21st century, in order to protect her while she became the unsuspecting human "Ruth Clayton" using a Chameleon Arch. He posed as her husband while they lived together in Gloucester. He was then seemingly executed by Gat, who had been hired to track down the "Ruth Clayton" Doctor. (TV: Fugitive of the Judoon)

Behind the scenes

 * Lee's species is not clarified in the episode, though there is certainly an implication that he is at least a Gallifreyan, as he shares Gat's training, and bitterly comments on human behavior under his breath.