Dahh-Ren (or 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.
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.