The Great Papyrus [Undertale]

Sans (brother)
Undyne (friend/mentor)
Flowey (friend)

Papyrus is a tall, perhaps anatomically inaccurate skeleton, with a skull more vertical and geometric than his brother. Being skeletal, many of his expressions incorporate a toothy grin. His eyes resemble vertical slits; his skeletal pseudo-brows form most of his expressions, as well as the corners of his mouth. He has eyeballs which show at times when he is experiencing strong emotions. Papyrus is relatively taller and slightly slimmer than his brother.
he wears his "battle body," an outfit that he created for a costume party.[1] It consists of an orange-red cape, a white chestplate with a gold trim on the bottom, and blue briefs with a golden belt. A symbol that resembles that of Starman from the MOTHER series adorns the chestplate. He also wears red coquelicot gloves, each with a yellow trim, and red boots.

Papyrus is a flamboyant skeleton who presents a confident, charismatic image of himself. He is thought to have an egotistical personality, referring to himself as "THE GREAT PAPYRUS," possibly as a way to feel as prestigious as his brother. He works hard and, despite his brash personality, is kind at heart. He is optimistic and brave, and is shown to be considerate and forgiving even when the protagonist beheads him in the Genocide Route.[3] He is also occasionally oblivious and nonobservant,[4][5] but can be cunning at times, as seen when he uses reverse psychology to trick Undyne into befriending the protagonist.[6] He is thought of to be somewhat naive by other characters, but not dumb. He shows great bravery as even in the face of potentially imminent death, he drops his guard and spares the protagonist hopes of driving them down a better path.

Papyrus believes in others just as much as he believes in himself. He has so much faith in his abilities that he waited outside of Undyne's house all night and begged her to accept him into the Royal Guard. Seeing his persistence, Undyne offered to train him, but instead gave him cooking lessons.[7]His confidence in himself and others is so great that he interprets direct insults towards him as the protagonist trying to make themselves look bad so he can hurt them easier, rather than the possibility that they dislike him.[8]

Sometime before the events of Undertale, Papyrus and his brother showed up one day in Snowdin and asserted themselves. Sometime after that, Papyrus became friends with Undyne and began training with her.