In Undertale

Sans is a skeleton wearing a blue jacket, black shorts with white stripes, and white slippers. Prior to the events of Undertale, he had moved to the settlement in Snowdin from an unknown location with his brother Papyrus. Papyrus was hired as a royal guard trainee sentry and forced his brother to help in his quest to capture a human.^[1]

Sans first appears in Snowdin, initially appearing as a silhouette approaching the player from behind before shaking the player's hand, setting off a whoopee cushion. He clarifies that he has no interest in capturing humans, unlike Papyrus, whom he describes as a "human-hunting FANATIC".^[2] After helping the player hide from Papyrus, Sans follows his brother throughout most of the forest, commentating on his puzzles and even contributing a word search, much to Papyrus's dismay. As the story proceeds, Sans continues performing such antics as attempting to sell the player highly overpriced fried snow.^[3] Later in the game, Sans invites the player to eat at a restaurant together. If they so choose, Sans explains how he befriended a woman, Toriel, behind the large door in Snowdin, who shared his love for puns. He reveals that he promised not to kill any humans who come to the Underground and states that if he had not made that promise, the player would have been "dead where [they] stand".^[4]

Sans makes one more appearance in the "Judgement Hall", where he reveals the true meaning of the "EXP" and "LV" values that the player has accumulated throughout the game: 'Execution Points' and 'Level of Violence', respectively. He judges the player for how high their EXP and LV values are before disappearing and allowing the player to proceed and fight the king, Asgore.^[5] After the player defeats Asgore and Flowey (if he has not been fought before) and they leave the Underground, Sans calls them to inform them of what occurred after their departure, having different dialogue depending on the player's actions in-game.^[6] If the player does not kill any monsters, Sans appears alongside the other main characters after the fight with Asgore is prevented.^[7]

If the player opts to kill every monster in each area, Sans's behavior will be different. Before the Papyrus boss fight, Sans threatens the player with a "bad time" if they proceed with their actions. If the player ignores Sans's warning and continues slaughtering every monster they meet, he eventually confronts the player in the Judgement Hall to prevent them from destroying all of the Underground, acting as the route's final boss. Sans is revealed to have supernatural abilities, able to somehow observe the various timelines created by the player's saving and loading (an action diegetic within the Undertale world), and wants to stop the player character before all the timelines are reduced to nothing.^[8] As the final boss, Sans is considered to be extremely powerful, but can be killed by the player.^[9]

In other media

Sans appears as a character in Deltarune, where, he can be found at his shop, a remodeled version of Grillby's Diner from Undertale.^[10] In Super Smash Bros. Ultimate, a Sans costume for the playable Mii Gunner character was released as downloadable content on September 4, 2019.^[11][12][13] In Among Us, Sans' hoodie appears as a cosmetic belonging to the Cosmicube event called "Indie Hour", also featuring other characters from Undertale.^[14] Sans has also been the subject of many fan works and projects, being featured in numerous games, creations, and video game mods.^[15][16][17]