Frisk

 is the playable character of Undertale, who attempts to escape the Underground and go back up to the Surface. They are the last of the eight humans to fall into the Underground after traveling to Mount Ebott.

They are not the fallen human the player names at the beginning of the game. Their name is revealed only during the ending of the True Pacifist Route.

Appearance
is depicted as a young human child of ambiguous age, gender, and ethnicity, with medium length straight brown hair, with a little bit of bangs and a blank expression. They wear a striped light magenta-and-blue shirt sometimes with a heart-shape, blue pants, and plain brown shoes.

While their sprites always show with a blank expression, the game often describes them making other expressions. For example, when cheers Napstablook in their battle, they are described as giving "a patient smile".

Personality
It should be noted is a "silent protagonist", designed so that the player is able to put themselves in their shoes. For this reason, their personality is not shown very well in the game by canon alone, and it is up to the player to fill in the blanks. talks to other characters, but unless the player receives a prompt on what to say, their dialogue is not shown. During battles, the flavor text describes what says. Outside of battle, when speaks on their own, often another character's dialogue box will display "..." to show that they are listening to.

Depending on the ending that the player is moving towards, can be depicted as friendly or cold. In the Pacifist Ending, characters such as Asriel make emphasized note about 's kindness, understanding, and grace. This is also the only ending when 's name is given, which implies that this is their true character and personality.

Abilities
has a great deal of determination, allowing them to save and heal at save points. When has a save file, they can load it from the menu screen, and will load during the game if they die. can also reset the world to when they landed in the underground, though this is not enough to completely erase the memories of others pertaining to what happened before the reset.

Neutral Route
Having landed in the Ruins, meets Flowey, who attempts to kill them and steal their SOUL. They are saved by Toriel, who guides them through the ruins and gives them a cell phone.

When reaches Toriel's home, they ask Toriel about how to exit the Ruins, making her leave with the intention of destroying the Ruins' exit. can either kill Toriel or convince her to let them leave the Ruins. Either way, begins a journey through the rest of the Underground.

Entering Snowdin Forest, meets Sans and Papyrus, who set up traps and puzzles in an attempt to capture them. When passes the town of Snowdin, they battle Papyrus, who tells them the exit of the Underground is in Asgore's Castle.

In Waterfall, is pursued by Undyne, head of the Royal Guard. meets Monster Kid while escaping from Undyne. After being chased through a number of rooms, falls into the Garbage Dump, where they receive a recollection from the first human. Here, they encounter Mad Dummy, who attempts to take their SOUL. On the end of Waterfall, battles Undyne, who tells them about Asgore's plan of destroying the barrier.

In Hotland, encounters the scientist Alphys, who upgrades their cellphone and guide them through the area. In Alphys's Lab, encounters Mettaton, who supposedly tries to kill them. walks across Hotland until they reach the Core, the only known way to the capital. At the end of the Core, Mettaton reveals Alphys's charade and attempts to actually kill and steal their SOUL.

Reaching the capital city of the underground named New Home, learns the story of Asgore and Toriel's children, Asriel and the first human, from monsters passing by. In the Last Corridor, Sans judges for the monsters they have killed, explaining the meaning of LOVE and EXP and telling them that they will decide the fate of the world.

Escape
enters the Throne Room and finds Asgore. Asgore tries to make small talk, but they remain silent. The two walk to the Barrier, and Asgore gives an opportunity to back out if they are not ready. Eventually, Asgore shows the six collected human souls to before they fight. Asgore temporarily prevents from showing any mercy to him, but after  defeats Asgore, they regain the opportunity to spare him, though they can kill him instead. Regardless of 's actions, Flowey will appear, destroy Asgore's soul, and take the human souls. The game then abruptly closes.

The player reopens the game, only to find that Flowey has saved his own game, having gained the power to do so with his stolen human souls. Loading Flowey's game, confronts Flowey and defiantly steps forward, entering an initially hopeless battle with him. calls out for help and the stolen souls begin to revolt: first they heal, then they weaken Flowey, leaving him vulnerable and eventually removing his ability to save or load. The souls leave and a weakened Flowey alone, and  has the choice of sparing or killing Flowey before they leave the underground. It is not explained how passes through the barrier, but it remains active and keeps the monsters trapped.

Some time after escapes, Sans calls their phone, leaving a message about what happened to the underground after Asgore died. None of the monsters know 's name.

True Pacifist Route
In order to complete the True Pacifist Route, the player must have first completed the Neutral Route.

If the player has completed the Neutral Route without gaining any EXP or LOVE (i.e. without killing anyone), Flowey allows the player to reload their save file so they can go back and complete any missing friendships, then achieve the True Pacifist ending.

If the player has gained EXP or LOVE in the Neutral Route, they will have to reset the game in order to achieve a True Pacifist Route.

Friendships
gains Toriel's friendship by sparing her, but she does not make another appearance until the end of the route.

gains Sans' friendship by sparing Papyrus, and can optionally hang out with him twice (once at Grillby's, once at the MTT Resort,) while gains Papyrus's friendship by visiting him at his home, and hanging out or dating him.

Napstablook can be befriended by smiling at them in the Ruins, and hanging out with them at their house. Befriending them is not required to complete a True Pacifist route.

If gave Undyne some water after being chased, they can befriend Undyne. visits Undyne with Papyrus' help, and Undyne gets "revenge" by trying to befriend, setting her house on fire in the process. She tries to fight to regain honor, but Undyne realizes that  is a "wimpy loser with a big heart" just like Asgore, and decides to become their friend.

Mettaton can be befriended by sparing him; survive enough turns without killing him.

Undyne, having been encouraged to send a love letter to Alphys, gives the letter to, who delivers it to Alphys. Alphys goes to the garbage dump and is encouraged to tell Undyne about her feelings for her, gaining 's friendship. Alphys tells Undyne that anime is not real, among several other truths, and Undyne asks if anime is real before leaving.

After befriending Alphys, Papyrus recommends that go to Alphys's lab. There, they find a note from Alphys, and enter the True Lab. She thanks for coming and gains the confidence to reveal the truth about her experiments to the rest of the underground. attempts to leave the true lab but they receive a phone call from a mysterious voice (later revealed to be Asriel), who mistakes for the first human, before the elevator breaks down again, and they are forced into New Home.

Barrier
Confronting Asgore again, and Asgore are stopped from fighting by the former's friends. Flowey appears, having stolen the humans' souls. He attempts to kill, but their friends use their magic to protect them. All of the underground's monsters arrive, falling into Flowey's trap of absorbing their souls. Only 's soul is left.

Flowey reveals himself to be Asriel, regaining his own form with the power of everybody's souls. He fights, and he continues to mistake them for the first human. , unwilling to fight Asriel, holds on to their hopes and dreams and refuses to die, preventing Asriel from gaining enough control over the timeline to reset it. They are trapped by Asriel, and realize that all they can do is save the monsters' absorbed souls. Saving their friends' souls by calling out their names and talking to them, regaining their memories, identifies one more friend to save, Asriel, and calls his name. sees Asriel's memories of the first human, who looked much like themself. Asriel starts to feel emotions from the monsters' souls, and eventually stops fighting, telling that he's afraid and alone.

Asriel, having realized that they are not the first human, learns 's name. He apologizes for hurting everybody, and has the option to forgive him. Asriel destroys the barrier with the souls before releasing them, and knowing that he will turn back to a flower, begins to leave; has the option to comfort him.

Freedom
wakes up with their friends (Toriel, Sans, Papyrus, Undyne, Alphys and Asgore). While the monsters remember little about Flowey and nothing about his incarnation as Asriel, they do know 's name. gets the opportunity to go through the underground and talk to the other monsters, including Asriel.

If speaks to Asriel for a final time, Asriel will ask them why they decided to travel up Mt. Ebott in the first place. Although does not answer - Asriel lists off foolishness, fate, and suicide as possible motives. Like the rest of 's personality, this is likely left open for the player to choose.

leaves the underground with their friends. Asgore offers them to be the monsters' ambassador to the humans. Most of 's friends then leave, except for Toriel, who asks what they will do now, and  has the choice of living with Toriel or not.

If chose to stay with Toriel, the ending scene shows Toriel bringing a slice of pie to 's bedroom. Otherwise, the game ends with a group photo of and their friends.

Genocide Route

 * See Chara for more information of this route.

Name
To "" means to skip or leap playfully, or to pat down on someone, looking for an hidden item. "" is the Swedish and Norwegian word for "healthy", and the Danish word for "fresh". "Frisky" means "playful and full of energy".

Naming the fallen human "" will initiate Hard Mode.

A pun for Frisk's name is "Pasi-Frisk."

Trivia

 * Maincharawalkd1fix.gif a joke thread on Starmen.net, Toby Fox posted early files from Undertale saying they were from an EarthBound hack called "UnderBound 2", where it was said that was planned to be a young androgynous child who was the step-cousin of "Squeezo" from the non-existent EarthBound hack, "UnderGround."  was also shown to have black outlines, darker hair and shoes compared to the lighter brown seen in the final version of the game.
 * and Flowey are the only two with the ability to SAVE, LOAD, and reset their SAVE FILE. Flowey is more proficient at this, as he can SAVE and LOAD multiple save states at any moment.
 * Chara might be capable of doing it too, though to what the extent is unknown, besides the fact that they can restore the world after the player gives them their SOUL.
 * While is allergic to Temmie, they seem unaffected by other furry residents of the underground.
 * As a hint that the fallen child is not, in official art,  has 6 stripes on their jumper, and not the one shown on the in game sprite of the Fallen Child.