Chara

 refers to a human child, the first of the Eight Humans to ever fall past the Barrier on Mount Ebott into the Underground. This person is in fact who the player is naming at the start of the game, and not the controllable character who is played throughout the entirety of Undertale.

Description
Chara is said to have looked incredibly similar to Frisk, down to a "similar fashion sense." Like Frisk, they are of ambiguous gender and appear to have also been around the same age as Frisk when they fell into the Underground.

True Pacifist Route
While initially cast in a sympathetic light by Asriel and others (primarily while they are talking to Frisk but using Chara's name), Asriel admits after being defeated in the Pacifist Route that the reason Chara climbed Mt. Ebott wasn't "very happy", and that they hated humanity, though they never explained why. He goes on to say that Chara "wasn't really a great person". It is hinted that Chara took pleasure in inflicting pain onto others, such as when Asriel mentions that Chara "laughed it off" when they accidentally made Asgore ill by putting buttercups instead of cups of butter into a butterscotch pie they made for him. Asriel even goes on to say that Chara took control of Asriel's body, picking up their own corpse and carried it out to a human village where Chara wanted to use Asriel's full power to kill the humans there.

Genocide Route
As revealed in the Genocide Route, Chara is seen to be wearing a similar but differently-colored striped shirt, and has rosy cheeks, open eyes, and a vacant smile.

The reincarnated Chara is cold and emotionless, not showing concern about the monsters the player killed and the world they destroyed. The only time they are mentioned is if the player restarts their game, but this is possibly an attempt to taunt the player due to the regret of their decision. Their speech is slow and silent, similar to Sans' threatening "voice". They talk in a rather sophisticated and malevolent manner, juxtaposition to their appearance and apparent age. They do show curiosity if the player chooses to not destroy the world, and after the player restarts the game and waits 10 minutes after.

Main Story
This first human fell into the Underground after the war between humans and monsters and was taken in by Toriel and Asgore as a second child, whom they treated with respect equal to their biological son, Asriel. Asriel quickly became friends with the fallen child, and grew to respect them greatly. Monsters of the Underground spoke of how Chara filled them all with hope.

One day, Chara became very ill, and requested to see the Golden Flowers of their home village once more. But because no one could cross the barrier, the request could not be fulfilled. Chara died the next day, and Asriel, wracked with grief, absorbed Chara's soul and became powerful enough to cross the barrier. He took Chara's body and carried it to a bed of flowers in the center of Chara's village. The villagers, believing Asriel had killed the human, began attacking him with everything they had. Although he had the power to destroy them all, he did not fight back; he smiled and carried the human back to the castle of New Home, where he himself died from his wounds. Chara was originally laid to rest in a coffin in the basement of the castle, in the same room in which the bodies of the other Six Humans would be laid after slain by Asgore. However, Flowey implies that Toriel carried the body to the Ruins to give them a proper burial.

Several points in the game, such as the VHS collection in the True Lab, imply that Chara's death was part of a plan that they had conceived: to poison themself with flowers, then for Asriel to combine their soul with Chara's to cross the barrier, then to collect the souls of six additional humans to gain enough power to break the barrier (though whether Chara's intention was benevolent is unclear; it could be inferred that the plan was to restart the war between humans and monsters). Asriel explains to Frisk at the end of the Pacifist Route that when his soul combined with Chara's, control over Asriel's body was split between them, and that it was Chara who carried their own body to the village. Chara also wanted to use their full power against the villagers, but Asriel resisted their influence and took control, returning back home instead, before his body perished to dust and scattered across the King's Throne Room with the seeds of Golden Flowers.

Neutral Route
If the player gets a Game Over then they will hear Asgore urging to "stay determined", with messages resembling that which he desperately told Chara while they were sick and bedridden. Asgore will sometimes tell Chara that "our fate rests upon you" and insist that "you cannot give up just yet".

The protagonist may also hear 's name in their dreams. When sleeping in Toriel's home. Asgore's voice can be heard, pleading "Chara, please... Wake up! You are the future of humans and monsters." When the protagonist first falls into the Garbage Dump, Asriel's voice can be heard talking to Chara as well. While walking through New Home, Frisk is told the history of and Asriel.

Before the Throne Room, there is a room with coffins for the seven humans that came before Frisk, and one of the coffins is for.

True Pacifist Route
In the True Lab, VHS tapes of Chara interacting with their family can be played back.

Before and after the final fight with Asriel, Asriel mistakenly refers to Frisk by Chara's name.

Afterwards, Asriel finally recognizes the protagonist as Frisk.

After saving Asriel, Frisk may return to the room containing the coffins of the seven humans before Frisk. They see that 's coffin is empty, and notice mummy wrappings at the coffin's bottom.

Genocide Route
The only instance in the game where Chara makes an in-person physical appearance, outside of flashbacks, is during and after a Genocide run, where the character plays an important yet somewhat ambiguous role. It is implied that, as opposed to playing as Frisk, you the player play as Chara inhabiting Frisk's body, who steadily grows in power by killing all of the monsters they can. Although almost everyone in the game recognizes the cold and malevolent behavior of the player in this route, only Flowey identifies the player as Chara, speaking to them like they have been friends for a long time, until Flowey realizes that he too may be killed.

Furthermore, Chara's voice and thoughts start to narrate the text that the player sees:


 * Examining Toriel's Home:
 * Kitchen: " Where are the knives. "
 * Examining various objects throughout Asgore's Home.
 * Padlocks: " He leaves them in the kitchen and the hallway. "
 * Beds: " My Bed " and " His Bed. "
 * Bookshelves/Asgore's Closet: " Nothing useful. "
 * Refrigerator: " No chocolate. "
 * Kitchen Note: " I've read this already. "
 * Photograph: " ... "
 * Journal: " The entries are always the same. "
 * Drawing of Flower: " My drawing. "
 * Closet: " Our clothes. "
 * Asgore's Dresser: " Still has that sweater. "
 * Mirror: " It's me, Chara. "
 * Real Knife:
 * Upon taking it: " About time. "
 * Flavor description: " Here we are! "
 * The Locket:
 * Upon taking it: " Where it belongs. "
 * When examining the coffin with the red soul on top: It's as comfortable as it looks
 * Several boss fights, as well as some miniboss encounters, show a significant change in tone when the player "checks" the enemy in battle as well.

After completing the first Genocide run, Chara will suddenly appear to address the player directly, saying they were brought back to life by the player's power and determination, and that the purpose of their reincarnation was power itself. They go on to identify themself as the very feeling the player receives whenever their stats increase, and implore the player erase the world so they can move on to the next.

The player is given a choice to "ERASE" the world, or "DO NOT". The player is unable to quit the game by holding down the Escape key, but they can quit or close the game using other methods. Regardless of the player's choice, will attack the screen, destroying the world. Disturbingly, Chara's eyes are missing, replaced with bloody sockets, and begins to cackle malevolently.
 * If the player chooses "ERASE", will call the player "a great partner".
 * Choosing "DO NOT" will cause a jumpscare (seen here), where tells the player that they were never in control, coming closer towards the screen with a horrifying facial expression while apparently laughing as the screen shakes and flashes to red and black.

speaks to the player if they open the game after completing the Genocide Route and leave the game open for 10 minutes. They sense that the player wants to go back to the game's world, and blame the player for causing the world's destruction. They offer to restore the world in exchange for the player's soul. Agreeing to this trade will restore the world, deleting the save file, but the pacifist ending will be permanently affected. Refusing will force the player to wait another 10 minutes, after which will offer the same choice again.

After completing the second Genocide run, Chara calls themself "the demon that comes when people call its name". They say that the reason the player continues to recreate and destroy the world is due to a "perverted sentimentality" they cannot understand, before suggesting that the player take a different path if they choose to create the world again. still gives the player the "choice" to erase the world, though it has the same results as the first time on the Genocide run.
 * If the player chooses "ERASE", will once again call the player "a great partner", saying they will be together forever.
 * However choosing "DO NOT" again will have tell the player that these very twisted feelings were exactly what they were just talking about. Chara then reminds the player they sold their soul a long time ago, causing another jumpscare, as they destroy the world again.

appears briefly if Pacifist run is completed after Genocide run, as they will have the player's soul at that point:
 * If the player stayed with Toriel, then the after-credits scene continues briefly after Toriel closes the door, showing in place of Frisk turning to face the screen with red eyes. The game cuts to black with laughter similar to Flowey's, but it is slowed down and lower-pitched.
 * If the player had "places to go", then the photo will have everyone's faces crossed out with red x's., who is in place of Frisk, does not have their face crossed out.

Trivia

 * Toby Fox, creator of Undertale, made a post on twitter suggesting the name of the Fallen Child to be the Player's own name.
 * The name "Chara" is used in-game and in promotional material regarding the game:
 * Naming the fallen child "Chara" results in the game saying that this is "the true name".
 * Removing the name from a save file results in the name "Chara" being given by default.
 * Two promotional gameplay screenshots have "Chara" as the name. Other materials leave the name blank.
 * "Chara" is likely just short for "Character," but there are speculations of its greater signifigance.
 * The word Chara (χαρά, ᾶς, ἡ) in Greek means "joy, delight, or gladness".
 * The child being "fallen" can refer both to the child having literally fallen into the Underground, or as part of a common phrase referring to having "fallen from grace" (i.e. having become morally corrupt).


 * Chara's soul is the same color as Frisk's, which can be seen on the empty coffin in the room down the hall from the throne room.
 * Chara is implied to like chocolate, since only during the genocide route, when the player looks at the refrigerator in Asgore's home, "no chocolate" is said in red text. This is not seen in the Neutral and Pacifist routes.
 * This line is more likely included as a pun on the phrase "bar none", meaning "no exceptions."
 * While Asgore's home contains no chocolate, there is, however, a bar of chocolate in the fridge at Toriel's home in the Ruins. It is possible Toriel kept her fridge stocked with it in memory of Chara's tastes.
 * The Heart Locket found in Asgore's home is implied to have belonged to Chara as opposed to Asriel. When the player finds the Locket in a Genocide Route and equips it, text that says "right where it belongs" is shown.
 * It can be guessed that Flowey had intended to use Frisk as a proxy to bring back Chara from the dead in order to fulfill their original plan. Hints of this appear in the True Pacifist route. Prior to the final battle, during the phonecall Frisk gets before exiting the True Lab, Asriel commentates on his and Chara's plan finally coming together. Also, during the end of the final battle, Asriel states that he did not want to part with Chara again after so long. A few more hints appear in the Genocide Route, as Flowey makes an alliance with Frisk, mistaking them for Chara. Flowey wanted to carry out a variation of their plan: to rid all of the Underground of life, steal the six souls that Asgore collected, and destroy the Barrier, a plan that came back to haunt Flowey as he realized in fear that his motto would not prevent Chara from killing him too when the time came. He attempted to convince Chara to call the plan off, but ultimately failed, and met his demise at the hands of his former surrogate sibling.
 * Chara ironically resembles the more upbeat characters from EarthBound Beginnings (Mother), EarthBound (Mother 2) and Mother 3, while hiding underneath their appearance a wicked entity.
 * Within the game files, there are sprites of Frisk wearing Chara's shirt and pants, lacking a face but having shading under the eyes.
 * It can be argued that Chara and Frisk are both in Frisk's body, but Chara only awakens if the player kills enough. Presumably Chara entered Frisk's body when they fell onto Chara's grave (the flower bed).
 * It seems that the creepy expression that Chara makes in front of Asriel in one of the tapes is the same face that Frisk seemingly does to the Monster Kid. Flowey also makes a face during the Genocide Route that could possibly be similar to the face that Chara makes during the jumpscare that happens if the player refuses to destroy the world.