Sans

Sans is a supporting character in Undertale as well as a minor character in Deltarune: Chapter 1. He is a skeleton monster, and the heroic final boss of Undertale's genocide route. Sans is the most popular and recognizable character from Undertale, and has achieved icon status among video game characters as a whole.

Biography
Sans is a skeleton monster living in Snowdin with his brother Papyrus. He first meets the fallen human when they leave the ruins, introducing himself with a prank. He explains that he has no interest in capturing humans, but his brother does. Sans appears multiple times as the human faces Papyrus' puzzle, helping out only on the lazily done word search. Later, when the human reaches Waterfall, Sans offers to take them out for lunch. They go to Grillby's, a pub in Snowdin. Sans question if the human has ever met a talking flower, and then explains that he believes someone his pranking Papyrus with an echo flower.

Later on, Sans once again meets the human in Hotland. He also, once agains, invites them to dinner, this time at MTT Resort. While at the table, Sans begins to tell the human about a woman he met at the door to the ruins. Sans says that she had him promise to protect any humans that leave the ruins, and that if it wasn't for this promise, the human would be "dead where [they] stand". Sans dismisses this as a joke, and leaves the resort.

The next time Sans and the human meet is in the Last Corridor, located in New Home. Here, Sans will judge the human based on how many EXP points they have. If the human has killed anyone, thus earning EXP, he will tell them to think about their actions. If the human as earned no EXP, meaning they have killed no one, he will congratulate the human on being compassionate and having mercy on the monsters they have met. Sans will let them pass, saying that one way or another, the human's choices will affect the world greatly.

In the True Pacifist route, Sans is absent from the corridor. He will later appear along with his brother after Toriel has interrupted the fight between the human and King Asgore. Sans, along with everyone else, is binded by Flowey's surprise attack. Sans and the rest of the human's friends will attempt to protect the human's soul from Flowey, until Flowey absorbs their souls. After Flowey has become Asriel, Sans will appear as a lost soul. After the human has defeated Asriel, Sans will leave the underground with everyone else.

In the Genocide Route, Sans will be absent from the game after the player kills Papyrus. In the Last Corridor, Sans will judge the player, and the proceed to enter a battle with them. In battle, Sans is called the "easiest enemy", and only has one HP. He will attack using various bones, like his brother, as well as the Gaster Blasters. Halfway through the battle, Sans will spare the human. If accepted, Sans will unleash an undodgeable attack and kill the human. If rejected, the fight continues. Eventually, Sans uses his special attack, in which he does absolutely nothing, forcing the game to be stuck on his turn. The human is eventually able to break the game and attack Sans anyway, killing him with one hit.

In Deltarune: Chapter 1, an alternate timeline version of Sans makes a cameo appearance. Sans is a resident of Hometown, and asks Kris to visit his brother sometime. He also mentions recently becoming friends with Toriel.

Appearances
*Appears as a DLC costume

Trivia
Despite being called the easiest enemy, Sans is often considered the hardest boss in Undertale. He even placed seventh on Screenrant's top twenty hardest boss fights.

Sans is often speculated to somehow be related to W.D. Gaster, a mysterious NPC in Undertale.