Papyrus' role can differ depending on the choices the player makes within the game. In the Neutral Route, he antagonizes the protagonist with puzzles and japes, but eventually warms up to him/her. He plays a big part during Undyne's encounter with the protagonist, and if the right choices were made, Papyrus will even flee from Undyne's house after using reverse psychology on her.
In the True Pacifist Route, it is necessary to befriend Papyrus in order to complete that route. He will also intervene the fight between Asgore and Frisk, while also being introduced to Toriel. When she makes a bad pun, it will annoy Papyrus, proclaiming that his best day ever has been ruined. He gets captured along with Frisk's friends by Flowey, who aspires to achieve his real form. When Flowey has been defeated, Frisk can decide whenever or not to lead Papyrus and the rest of the gang up to the surface.
In the Genocide Route, Papyrus will still engage in his usual shenanigans. However, he will get concerned about the player character's murderous intentions. He/she can decide whenever to spare Papyrus or kill him.
Papyrus received a lot of really positive feedback from fans of the game. Many fans also enjoy his hilarious, but innocent and naïve nature.
Many fans may even relate to him and his hobbies, which can include childish, but fun things the character himself enjoys doing in his spare time.