The Underground’s Royal Scientist. Alphys is brilliant but anxious, obsessed with anime and human culture, and burdened by the consequences of her Determition experiments.

The kind but tragic king of the Underground. Asgore seeks to break the barrier trapping monsters by collecting human SOULs, but he deeply regrets the path that led to war.

The prince of monsters and son of Asgore and Toriel. Asriel’s story is tied to the first fallen human and to Flowey; in the True Pacifist route, he becomes the fil boss with overwhelming power.

The first human to fall into the Underground. Chara was adopted by the Dreemurrs, and their legacy is closely tied to the game’s darkest route and rrator-like presence.

A sentient flower with no soul who manipulates events from the shadows

A human child who falls into the Underground. Frisk’s actions—mercy, violence, and everything between—shape how monsters respond and which ending the world reaches.

A ghost who inhabits a robot body built by Alphys. Mettaton is a glamorous star in Hotland, hosting shows and chasing fame—with multiple combat-capable forms.

An enthusiastic young monster from Waterfall who idolizes Undyne. Monster Kid is brave in spirit, often trying to do the right thing despite being outmatched.

A shy ghost found in the Ruins. pstablook prefers quiet hobbies like listening to music and making lo-fi tracks, and can become a gentle encounter depending on your choices.

Sans’s enthusiastic younger brother. Papyrus is earnest, dramatic, and determined to join the Royal Guard by capturing a human—yet he’s also genuinely kind.

A laid-back skeleton known for bad jokes and sharp observations. Sans acts as a moral judge of the player’s actions—and becomes a deadly opponent on the Genocide route.

A quirky Temmie from Temmie Village in Waterfall. Temmies are known for their odd speech patterns, humor, and the Tem Shop.

The former queen of the Underground who lives in the Ruins, protecting any fallen humans. Toriel is gentle but firm, and she refuses to accept more children dying for the barrier.

The fierce captain of the Royal Guard. Undyne is bold and heroic, initially hunting the human for Asgore’s cause—yet she can become one of Frisk’s strongest allies.

A hidden figure associated with rare events and corrupted text. The game implies a connection to a former Royal Scientist, but most details about W.D. Gaster are intentiolly unclear.