Not much is known about Papyrus' background. All we known is that his brother and himself suddenly showed in Snowdin one day and asserted themselves. For a very long time, Papyrus has wanted to join the Underground's Royal Guard, and even trains with their leader, Undyne, on a regular basis. While Undyne actually considers him a good fighter, she believes Papyrus is too nice to do some of the more violent work of a Royal Guard, so she doesn't make him one. One day, Papyrus and Sans encountered a human child, who'd fallen into the Underground, and tried to capture them and bring them to King Asgore. After using numerous puzzles to try and capture the human, followed by battling them himself, Papyrus instead befriended them, and wished them luck on their journey.
Papyrus is a tall, perhaps anatomically inaccurate skeleton with a skull shaped in a more straight and geometrical structure (in contrast to his brother's more rounded skull). His mouth is in a smile shape most of the time and his eyes are pupil-less, resembling vertical slits with his expressions being formed mostly by his skeletal pseudo-brows. He stands at 6 feet tall.
He wears a custom-made costume known as his "battle body", which is made up of a white torso piece with various golden trims (and embroidered with a symbol that very heavily resembles that of the Starman from the Mother series), a rough red scarf or cloth around his neck, red gloves (trimmed with gold), blue briefs with a golden belt, and long red boots.
Papyrus is eccentric, flamboyant, naive, self-absorbed yet kind and, formely, initially appears to have an inflated ego. Though he is at first obsessed with capturing a human and accomplish his dream of becoming a Royal Guard, he truly cares about those around him like who talk to him and just want to be friends with him, being Frisk the only human who he encountered like a genuine friend. Papyrus also has a good relation with his older brother Sans, though sometimes both disagree with their habits such like Sans being lazy at his work and being more careless than Papyrus. Papyrus also finds it annoying when Sans leaves one of his dirty socks lying around in their living room. Papyrus finds puns to be very annoying as shown by his interactions with Sans and Toriel.
Papyrus however, is also very innocent as he believed Sans when he said that Undyne along with other monsters went to vacations in a neutral ending where Frisk killed them and Papyrus became the ruler of the Underground. He admits that he wants to be everyone's friend. He is also shown to be determined at his dreams as he begged to Undyne to let him be a Royal Guard so she decided to train him to become one, even if she thinks he can't be able to be one because of his innocent and optimistic attitude towards others (Although it is unknown why he chose to visit Undyne at midnight.) He also believes that everyone can be a great person if they just try, as shown when, on the Genocide Route, he believed that Frisk could be redeemed even though they had killed over 30 monsters by then. He even immediately spares him and offers to be his friend and mentor. Even if Frisk decides to kill him then, he held on to his belief that Frisk can become a better person.
Papyrus is unique compared to most of the other characters in-game, being that he speaks exclusively in Capital Letters, as though he is always shouting. He does so in his namesake font, like his brother Sans.
- Papyrus' clothes are actually a costume him and Sans made for a party once, and he hasn't removed them since.
- Temmie Chang's artwork for the game depicts Papyrus as being 3 times taller than Sans.
- Papyrus can be considered a minor as he dates the main protagonist of the game, who is a child.