Steadfast was part of a crew of human colonists who had settled on a planet in the far future.
When he awoke from stasis, he met the Twelfth Doctor and Bill, who told him that the Vardies had killed the entire set-up team. However, instead of listening to the Doctor entirely, Steadfast and a few other colonists armed themselves and decided to kill the robots who they thought were a threat. When two Emojibots were about to kill Praiseworthy, he shot one of the robots, which led the Vardies above them to attack in retaliation. Once the Doctor reset their memories, he began negotiations between the humans and the Vardies who were willing to let them live in the city. (TV: Smile)