Dahh-Ren

Dahh-Ren was the only non-human survivor at Chasm Forge. He disliked being called "Darren", and accused Bill Potts of being racist, in response to his blue skin.

He was eventually killed after the walking corpses in smartsuits activated his own smartsuit to kill him. (TV: Oxygen)

Behind the scenes
Behind The Scenes sources differ as to whether Dahh-Ren is human or belongs to a non-human species. The official Doctor Who website describes him as a "non-human". . Actor Peter Caulfield says in the Series 10 documentary Being "Blue Peter" that he is a human who is "genetically different".