Sans is a rebel in the fight against homeworld, he is apart of the "Crystal Monsters" which is lead by Toriel, and the following members include: Undyne, and Papyrus.
Sans' appearance is a humanoid skeleton body that is red, he has a red gem on his head, he wears black sports shorts, wears a red jacket, and wears slippers.
Sans' personality is a relaxed, kind, and funny personality. He wants everyone to hear his bad puns.
Sans was created in the Alpha Kindergarten near the CORE, he watched by King Asgore, and was sent into battle to fight the humans, before the humans made a barrier. Afterwards, Sans decided to leave the army and join his brother, Papyrus, in Snowdin and stay there for decades. He ditched his homeworld suit, and wore a red jacket to hide his past so no one can report him.