Sans

Sans is a supporting protagonist who helps Frisk in Undertale. He is the short and big-boned brother of Papyrus who is usually lazy and laid-back. Sans also has a liking for bad jokes and puns, and uses them often.

Trivia

 * Sans is normally seen as wearing slippers, but his official artwork reveals they're simply sneakers - different colored parts of the sneaker on his ingame sprites simply make it appear as a slipper.
 * Sans is suspected to be a time-traveller as a strange machine is in a secret room in his house. Also, he has knowledge of previous events if the player resets the game.