Dahh-Ren

Dahh-Ren worked for Ganymede Systems aboard Chasm Forge. His smartsuit was off network when the remaining suits received a command to deactivate their living components. He was therefore one of the four survivors present when the Twelfth Doctor arrived aboard the station. He was the only non-human survivor aboard Chasm Forge.

He disliked being called "Darren", and accused Bill Potts of being racist, in response to his blue skin.

He was eventually killed in Chasm Forge's Section 12 when the smartsuits instructed his own suit to disable its organic component. (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".

The appearance of Jorj in World Enough and Time, who is strikingly similar to Dahh-Ren, would suggest that he is non-human. Additionally he shares an appearance similar to that of crespallions, first seen in The End of the World.