Papyrus was an agent of Giygas, serving him. After Giygas defeat, Papyrus was warped to the Underground. There, he finds Sans, which was his brother. They lived together, but later, Papyrus hated Sans at times. He thinks Sans is "Lazy, and he never captures a human!". This was because of his greed of wanting to join the Royal Guard.
Then, Papyrus found Frisk. He was very happy as it was the first human he'd seen. Papyrus kept setting traps for her, but Frisk overcome them. Once Frisk was leaving Snowdin, Papyrus challenged her. Frisk accepted but never attacked. Papyrus was amazed how well Frisk can dodge his attacks, even in her blue state.
Papyrus was a skeleton that had a Starman suit on. He had a cape, and boots. Despite him being younger than him, Papyrus was taller than Sans.
Papyrus is the exact opposite of Sans. He is very active, and never accepts a defeat. he hates slackers but does have a liking of puns.
Papyrus uses attacks similar to Sans. He doesn't have Gaster Blasters, but Papyrus has bones and an attack to turn human hearts blue, like him.