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 it's organic component. (TV: Oxygen)
Personality
Dahh-Ren managed to keep a calm and level-headed attitude during the frightening and terrible events occurring aboard Chasm Forge. However, he appeared to be sensitive or easily irritated when it came to his skin color, instantly misinterpreting Bill’s attempt to say hello in an alien manner as being a racist approach. Despite getting off on the wrong foot, he quickly warmed up to Bill and the Doctor and remained loyal and helpful right up to his unfortunate demise. (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".[1]. Actor Peter Caulfield says in the Series 10 documentary Being "Blue Peter" that he is a human who is "genetically different".[2]
The appearance of Jorj in World Enough and Time, who is strikingly similar to Dahh-Ren, would suggest that he is non-human.