Names

Names played a large part in the fictional universe, especially in stories with the choose-your-own-ending aspect. The Player was asked to name a character chosen by the author; this character was particularly the controlable protagonist and had the ability to SAVE and Reset, although this was not always the occasion.

Undertale
At the beginning of Undertale, the player was given the choice of naming the fallen human.

Normally, the Chara asked "Is this name correct?" when asking for confirmation of the name, but some names triggered a unique response, and some of these names (mainly those of major characters in the story) could not be used; however, all forbidden names could be used in the Undertale Demo. Other names did not trigger any particular message but had a different impact on the gameplay. There was a six-character limit, but this could be bypassed using the renaming process as seen below.

Although this was depicted as the player naming the protagonist, it was, in fact, naming the first human to have fallen into the Underground. This name was mentioned by Flowey/Asriel, Asgore in the game over screen, the dream sequences in Toriel's house and Waterfall, the mirrors in Toriel's and Asgore's houses on a Genocide Route, the video recordings in the True Lab, and the first human's coffin. Notably, none of the characters ever spoke the protagonist's name until they learned about it in the True Pacifist Route ending.

All names (except "Frisk") could not be changed without performing a True Reset or completing a Genocide Route. Otherwise, when resetting, the message from Chara "A name has already been chosen" appeared and the player was unable to change the name. "Frisk" was the only exception, as changing the name was required to leave Hard Mode.

Names with a Custom Response
Below are listed names that would give a custom response, replacing the default one. Alphabetic characters were case-insensitive and kana are script-insensitive. When played in Japanese, due to being able to enter both kana and alphabetic characters, the same response would occur regardless of whether the English or Japanese name was entered.

Names with Other Effects

 * Drak or Gigi or Gugu - The Steak in the Shape of Mettaton's Face showed up as "FSteak" instead of "FaceSteak". This name was a reference to Gigidigi's Persona 4 comic, "Hiimdaisy". Notably, Gigidigi has also helped work on the game.
 * Gaster or ガスター - In the original PC versions, the game reloaded the title sequence after pressing the confirm button; in the latest version, the game reloaded as soon as the last character of "Gaster" was entered. In the original PlayStation 4 and Vita versions, the game crashed and displayed an error message when entering "Gaster"; in the latest version, it simply reloaded the title screen. If Chara's name was changed to "Gaster" through the SAVE files, the ability to Reset would be unavailable as the game would restart upon clicking the Reset button.
 * Frisk or フリスク - In addition to having a custom response, this name activated Hard Mode.

Changing the Name in the SAVE Files
Normally, the name could not be changed except after a True Reset or giving your soul to Chara. However, it was possible to change the name during gameplay by modifying the game data. If the game detected that the name had been edited (for example, if it is longer than six characters), Chara gave the message "Easy to change, huh?" in the stats menu. Oddly enough, this did not occur if a forbidden name was used.
 * 1) Go into "%LOCALAPPDATA%\UNDERTALE" on Windows (e.g. "C:\Users\YourName\AppData\Local\UNDERTALE") or "~/Library/Application Support/com.tobyfox.undertale/" on Mac.
 * 2) Open the file named "file0" with a text editor of choice.
 * 3) The name is stored on the first line. Replace it with a new name. Numbers and symbols can be added to this new name, but if it is longer than six characters, it covers surrounding text. Using a forbidden name has no effect.
 * 4) The name is also stored in undertale.ini and is displayed when loading a SAVE file, but it is be overwritten with the file0 name when the game is saved if they are different. If the game is reset instead of loading a SAVE, the undertale.ini name will overwrite the file0 name instead.