Sans was one of the assistants that helped the previous royal scientist Dr. W.D. Gaster build the CORE. Sans was in charge on entering the entries on the experiments, copying down what was on Dr. Gaster's mind. The CORE's building was successful, so Dr. Gaster decided to work on another creation. But during mid-creation, Dr. Gaster was sucked into the project, ripping through space and time, turning into nothingness. The Gaster's followers was disbanded, rarely ever seen by monster-kind, with the exception of Sans. Nobody in the underground bother to acknowledge the Gaster's followers, and mainly took the credit to Dr. Gaster. Sans, however, didn't believe he had the responsibility to become the Royal Scientist, so the job was given to Alphys. Sans decided to move into Snowdin along with his brother Papyrus, to start a new life. There, Sans decided to work on his own creation, the Timeline Machine, and from there on, he would be able to teleport to different timelines.
Sans looks the same as he does in Undertale, with the exception of his clothing. Sans wears a light blue lab coat, dark grey sweatpants, a yellow bow-tie, and unlaced blue sneakers with white toes.
Compared to his Undertale counterpart, Sans is more open to his interest in science, though doesn't talks about timelines and such to his peers, due to their unawareness of them. Sans seems to be lazy in the outside world, but when he's on his research, Sans doesn't slack around and more focuses on his work. Sans takes a lot of enjoyment on humor, and always gets a kick out of cracking a pun or playing a prank.