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.
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. (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".