Player
And UNDERTALE TEAM thanks you, the player, from the bottom of our hearts. Without you, all of this would be impossible.
The player is the real-world individual playing Undertale and controlling the protagonist by moving the protagonist's physical body and SOUL.
Before the player starts the game, they name the fallen human and not the protagonist.
The duality of the protagonist and the fallen human is not revealed until the epilogue of the True Pacifist Route[1] or (if slightly less clearly) the Genocide Route. Throughout the game, characters do not refer to the protagonist by name and instead call them "human" or "child".
On the Genocide Route and the True Pacifist Route, Flowey calls the protagonist by the player's chosen name. Flowey/Asriel is the only character to do this; Asriel names his best friend in the True Lab's VHS tapes and before the battle against him.
LV relates to the number of monsters killed, and higher levels of LV make it easier to harm others.[2] Because LV and EXP display under the player's chosen name in the Stats menu, they increase the fallen human's ability to harm others.
At the end of the Genocide Route, the protagonist does not require a SOUL to attack. The player loses control over the protagonist as they autokill Asgore and Flowey. The bullet board does not appear for either of these encounters.
At the end of the Genocide Route, the fallen human addresses the fourth wall. Whether they are speaking to the protagonist or the player is unclear, as their speech could be applied to either.
While the player usually conducts the protagonist's actions, there are cutscenes in the Neutral Route and the Genocide Route in which control of the protagonist is temporarily disabled, and the protagonist performs actions independently from the player.
- When Toriel asks for the protagonist's hand, they comply and let themself be guided through the false spike puzzle without a player prompt.
- At Toriel's Home, the protagonist lets Toriel bring them towards the guest room in the hallway.
- If the protagonist did not ask how they can exit the Ruins and attempts to go into the basement, the protagonist allows Toriel to bring them back upstairs.
- During Sans's introduction, he instructs the protagonist to go through the bridge after telling them about Papyrus. The protagonist crosses the bridge on their own, with Sans following closely behind. This also occurs on the Genocide Route.
- The protagonist automatically hides behind the conveniently-shaped lamp when Sans directs them to it and comes out when he tells them to.
- The protagonist automatically follows Papyrus as he leads them to his house.
- In Papyrus and Sans's house, the protagonist attempts to catch the Annoying Dog as it escapes from the sink leading to the Dog Shrine.
- During the hangout with Undyne at her house, the protagonist follows Undyne to the stove during her cooking lesson.
- In New Home's Throne Room, the protagonist walks forward on their own, alerting Asgore as he is watering the golden flowers. This also occurs on the Genocide Route.
- Before the battle with Omega Flowey, the protagonist takes a step forward as if to defy him.
- The protagonist does not hide behind the conveniently-shaped lamp when Sans asks them to.
- During the puzzles with Papyrus, the protagonist seems to ignore Papyrus, and walks forward independent from the player.
- During the confrontation with Papyrus, the protagonist continuously walks forward on their own, and Papyrus notices and comments on it.
- Before the battle with Undyne the Undying, the protagonist turns away and then approaches Monster Kid aggressively.
- During the two encounters with Mettaton, he notices the protagonist's eagerness to fight him.
- During Sans's judgment, the protagonist takes another step forward as if to provoke him into fighting.

- With no player input, the protagonist deals the killing blow to Sans after he dodges the player's final attack, dealing 9999999 damage.[note 1]
- In the Throne Room, the protagonist forcibly engages in combat with Asgore.
- The protagonist then attacks Asgore, dealing 9999999999 damage.[note 1]
- After Flowey begs for mercy, the protagonist repeatedly attacks him until he is no longer visible.[note 1]
- 1 2 3 The attack animation that plays is the exact same as the Real Knife even if the player does not have it equipped.