Undertale and Deltarune are fantasy role-playing video games developed by Toby Fox. They take place in different fictional universes, but feature many of the same characters. Undertale is set in a world where monsters once coexisted with humans on the planet's surface, but, after an ancient war, were trapped in the Underground and forgotten. The game follows Frisk, a human child who falls into the Underground via an opening adjacent to Mount Ebott, and seeks to escape.
In Deltarune, considered a spiritual successor to Undertale, humans and monsters still coexist. Set in Hometown, the game follows Kris, who discovers a Dark World, an alternate view of reality inhabited by Darkners, living representations of real-world objects. They embark on a quest to close the Dark Fountains giving these Worlds form before darkness overtakes the real world.
The following is a list of major characters who appear in one or both games in the series. The characters have been praised by critics and fans for their humor and in-depth characterization shown through different moral choices. Some characters gained notoriety for their ability to break the fourth wall, manipulating gameplay elements normally only accessible to the player, such as saving.
Creation and conception
Toby Fox is the lead designer, writer, and primary composer for Undertale and Deltarune, while Temmie Chang and other guest designers design the characters. For Undertale, Fox felt it was important to make each of the game's monsters "feel like an individual". He cited the Final Fantasy series as the opposite; "all monsters in RPGs like Final Fantasy are the same ... there's no meaning to that".
Undertale and Deltarune Toriel and Asgore Dreemurr
Toriel, a powerful goat-like woman (belonging to a race known as the "Boss Monsters") living in the Ruins, is among the first characters met by the protagonist. She is the former queen of the Underground, where monsters live. Her ex-husband is its king, Asgore, with whom she had a child, Asriel, and adoptively raised a human child, Chara.
After Chara's untimely death, Asriel wielded their soul to cross the barrier and return their body to the surface, but was killed by humans in the process. Enraged, Asgore determined to collect human souls over time from those entering the Underground, until he would have enough to free monsterkind and take revenge on humanity. Toriel, sickened by her husband's obsession and cowardice, departed to live in seclusion among the Ruins below Mount Ebott. She takes the protagonist in after they fall into the Underground, and she attempts to keep them from leaving due to the worry that her ex-husband would hurt them; she is either killed or persuaded to let the protagonist leave.
Asgore awaits the protagonist at the end of their journey, where they are forced to battle. Asgore only survives in the game's "True Pacifist" route; otherwise, he is killed by either the protagonist or Flowey.
As Boss Monsters, once Toriel and Asgore have children, they only grow alongside their children, and cease to grow if their progeny disappears or dies.
In Deltarune, Toriel and Asgore are also separated. They are the parents of Asriel and the adoptive parents of the main protagonist, Kris. Kris lives with Toriel, a teacher, while Asgore, formerly Hometown's chief of police, lives apart from them at his "Flower King" flower shop. After an as-yet unspecified incident involving a Dark World, Asgore was fired from the police and became obsessed with collecting evidence to clear his name, straining his relationships. Mysteriously, the Knight attempts to kidnap Toriel and Asgore, failing to take the former in her sleep in Chapter 3, but succeeding with the latter in Chapter 5.
Asriel Dreemurr
In Undertale, Asriel is the deceased son of Toriel and Asgore, and the former prince of the Underground. Chara, his adoptive human sibling, convinced him to participate in a plot to collect six human souls from the surface, starting by them killing themself. After absorbing Chara's soul and leaving the Underground, Asriel refused to fight back against the humans who mistook him for Chara's murderer and was killed by them. Asriel was later reincarnated as Flowey by Alphys, but without a soul, he lacks empathy and compassion in this form. In the game's "True Pacifist" route, Flowey transforms into an adult representation of Asriel, known as the "God of Hyperdeath," serving as the final boss of the route. After being defeated, Flowey temporarily reverts to the child form of Asriel and regains his empathy, long enough to share a tender moment with the protagonist and break the Underground's barrier.
Jason Schreier of Kotaku called Asriel's final boss fight one of the greatest in video game history, citing its climactic music and the necessity to save your friends from him. Describing the sequence as "spectacular", he stated that, "if you're not already bawling as you mash the SAVE button over and over again during the final part of this fight, well... you will".
In Deltarune, Asriel is Kris's adoptive older brother who has left for college. He has not yet made a physical appearance in the game, but has been referenced numerous times with characters anticipating his return to Hometown.
Sans and Papyrus
A pair of skeleton brothers known for their outlandish human-capturing schemes, Sans and Papyrus primarily function as comic relief within Undertale. They are respectively named after the typefaces Comic Sans and Papyrus, which they use in their dialogue, with Papyrus speaking in all-uppercase, and Sans mostly speaking in all-lowercase.
Papyrus is egotistical yet incompetent, though Undyne claims he is "pretty freaking tough." He has a fondness for puzzles, and is desperately lonely, wishing to capture a human to join the Royal Guard and improve his "friend quantity". Despite this, he is shown to be a kindhearted and genial character who believes that anyone can be good if they try.
Sans is a clever, laid-back slacker and trickster. He often pulls practical jokes and enjoys making puns, and he bonds with Toriel over their shared love of the latter. Sans also frequently breaks the fourth wall, occasionally alluding to an understanding of the world's manipulation by the player via save files. At the end of Undertale, before the protagonist faces Asgore, Sans "judges" the player's morality, and in the "Genocide" route, he acts as the final boss himself, where he manipulates some of the game's mechanics against the player.
In Deltarune, Sans runs a grocery store in Hometown known as 'Sans, and is shown developing a close friendship with Toriel. Sans additionally mentions that he has a brother, whom he expresses a desire for Kris to meet. This is implied to be Papyrus, but his whereabouts are not revealed as of Chapter 5.
Undyne
In Undertale, Undyne is the powerful leader of Asgore's Royal Guard. She is humanoid with fish-like features. While initially presented as intimidating, her clumsy behavior in combat is heavily inspired by anime, which Alphys has convinced her is an accurate representation of the human world. She possesses a small amount of Determination: a substance that makes humans far stronger than monsters and enables her to persist upon death. Compared to Asgore, who harbors remorse for killing others, Undyne holds a deep hatred for humans and will not hesitate to kill them, although this lessens if the protagonist befriends her.
In Deltarune, she serves as Hometown's chief of police after Asgore was fired. She lacks an eyepatch over her right eye from Undertale and only knows Alphys in passing. In Chapter 3, Undyne enters the Dark World of the Dreemurr household just in time to rescue the party and Toriel from the Roaring Knight. However, she is quickly snatched away by the Knight and brought to the locked shelter south of Hometown, with Susie resolving to break in and rescue her.
Alphys
In Undertale, Alphys is Asgore's Royal Scientist and Undyne's love interest. She is a shy, nerdy, lizard-like monster with low self-esteem, and is a heavy otaku. She created Mettaton's robot body in order to make Asgore think she was capable of creating artificial souls to gain the position of Royal Scientist. She and Mettaton manufacture problems for her to solve for the protagonist and gain their trust, though Mettaton later rebels and attacks the protagonist outright. Alphys succeeded W.D. Gaster as Royal Scientist after his mysterious disappearance.
Undertales "True Pacifist" route reveals that she experimented with Determination on comatose monsters, but this caused them to melt and fuse with each other into creatures known as "Amalgamates"; she keeps them locked away in a hidden "True Lab". The same series of experiments resulted in the creation of Flowey, after Alphys injected Determination into a flower that had Asriel's dust on it.
In Deltarune, she is a teacher at Kris's school and is also infatuated with Undyne, but from afar.
Napstablook
Napstablook is a shy, apologetic, and insecure ghost with an interest in music production, who lives alongside the monsters in both Undertale and Deltarune. Their dialogue is written using exclusively lowercase letters, along with frequent and lengthy ellipses.
In Undertale, Napstablook first appears in the Ruins as the game's first miniboss encounter, then reappears in Waterfall to interrupt the battle against Mad Dummy. They can be found from then on at their nearby home, where they own and operate the Blook Family Snail Farm. There, the player can participate in a snail-racing minigame run by Napstablook called "Thundersnail". Hidden diaries belonging to Mettaton refer to Napstablook as his "cousin", and reveal that they were close friends before Mettaton became famous. If Mettaton is defeated through non-violent means during his boss fight, a phone call from Napstablook inspires Mettaton to remain in the Underground instead of escaping.
In Deltarune, Napstablook works as a police officer for Hometown's police force alongside Undyne, and participates in the town's annual Festival during Chapter 5.
Gerson Boom In Undertale, Gerson is an elderly shopkeeper in Waterfall. He was once a hero known as the "Hammer of Justice" and fought in the war against humans. He was at one point a mentor of Undyne's. Optional dialogue during the game's "Genocide" route indicates that Gerson has some awareness of his existence as a video game character, as he knows he cannot be attacked while he is within his shop.
In Deltarune, Gerson was a local historian and fantasy author who died before the start of the game. In Chapter 4, a Darkner greatly resembling Gerson, simply referred to as the Old Man, appears in a Dark World as the personification of an item from Gerson's burial ritual that was exhumed from his grave. The Old Man operates a small shop and spends most his time writing a letter of encouragement to Gerson's son, the local priest, which he later gives to Susie to rewrite in the Light World. He also encourages and mentors Susie, helping her improve her healing magic and adopting the "Hammer of Justice" persona to duel with her as the chapter's secret boss. At the end of the chapter, the Old Man reappears to help the party defeat a Titan.
Mad Mew Mew Mad Mew Mew is the name given to a recurring ghost character who appears in both Undertale and Deltarune. Like other ghosts in the setting, she is an incorporeal being who seeks to attain a physical form by possessing an ideal object. Mad Mew Mew has an egocentric and short-tempered personality, and a speech quirk of repeating the same word or phrase three times in a row with increasing emphasis. She is cousins with Mettaton and Napstablook.