Papyrus

Papyrus is one of the main characters in Undertale.

The player is first introduced to Papyrus soon after meeting Sans outside of the Ruins, wherein Sans says they are brothers. How the rest of the encounter, and the player's interactions with Papyrus throughout the game, plays out is affected by the route the player is taking.

In the Genocide route, despite the player not responding to Sans telling them to hide behind the lamp, Papyrus doesn't even acknowledge them standing out in the open as Sans states that he has indeed seen a human, leaving just as quickly as he came. Later on, the player will meet Papyrus again past the Box Road where he's initially talking with Sans about when the human is going to appear. When Sans suggests that he look in the direction your just coming from, Papyrus initially thinks he's talking about the rock behind the player and still doesn't know who, or what, the player is until Sans helps him use the process of elimination. Papyrus will then warn the player, in the playful manner, that they will face many puzzles and risk being captured if they proceed any further. When the player reaches the Invisible Wall Maze puzzle, Papyrus will attempt to explain how it works only for the player to just walk up to him through the puzzle area before it can be activated. Past that area, the player will run into Papyrus and Sans again with "obstacle" of a cross-word puzzle before them. Ignoring the puzzle, Papyrus will point out that it did nothing and Sans will comment that he should have gone with a "Junior Jumble" puzzle instead, which is Papyrus' favorite. Further along, the player will come across several more of Papyrus' puzzles but they will be unactivated. When the player reaches the Colored Tile Puzzle, Papyrus will attempt to explain the puzzle only for the player to once again just walk through it before it can be activated. After talking with Sans, Papyrus will ask the player a question, but they won't respond. To this, Papyrus decides to leave the instructions for the puzzle for the player to look at and do it themselves. When the player reaches the bridge to Snowdin, Papyrus will prepare a more deadly trap for you but will decide not to activate it since the player just walked through all of his puzzles. Finally, when the player is about to leave Snowdin for the Waterfall area, Papyrus will confront them about their behavior including how they walk around with "powder" on their hands. Unaware of what the player has been doing, Papyrus will believe that they are simply starting to lose their way and will offer to be friends so that they will stay on the "straight and narrow." But even after the player kills him, Papyrus will still believe that they can be a good person.

In the Genocide route, if the player spares Papyrus then they won't have to battle Sans at the end. Likewise, if the player takes the Neutral route and kills Papyrus, they won't have to battle Sans but he will make his anger about it clear.

In the Pacifist route, the player will listen to Sans and hide behind the lamp just before Papyrus arrives.