The protagonist of the game, whose gender is left ambiguous. Frisk falls into the Underground and spends the game trying to find a way back to the surface.
A flower-like monster that the player encounters early in the game. It guides the player in how to play and also imparts some twisted lessons.
The guardian of the Ruins, who rescues the player from Flowey and guides them through the early parts of the game.
The king of the Underground, who is gentle and seeks to reunite monsters with the surface world.
Papyrus's lazy, skeleton brother who is not particularly interested in catching humans.
Sans's enthusiastic, skeleton brother who is desperate to join the Royal Guard by capturing humans, despite not harboring any hatred towards them.
A tough, fish-like monster who is the captain of the Royal Guard and is relentless in her pursuit of humans.
The royal scientist, who is shy and has a stammer, and is responsible for creating Mettaton.
A charismatic robot designed to entertain and kill humans, who becomes a central figure in the game's events.
The prince of the Underground, Asgore's son, and a key character in the game's narrative.
Frisk's fallen human sibling, who plays a significant role in the game's backstory and is connected to the Genocide route.