Sans is a fictional character created by Toby Fox for the 2015 role-playing video game Undertale. Initially appearing as a friendly NPC, he later becomes the de facto final boss if the player chooses to complete the "genocide route" and destroy the game's race of monsters. His name is based on the Comic Sans font, which is used for most of his in-game dialogue. The character was praised by critics for his dialogue and boss fight, which is considered to be the most difficult in the game. His popularity with fans inspired several user-created mods and other types of projects.

More facts here: https://en.m.wikipedia.org/wiki/Sans_(Undertale)