The Player, also referred to as "The Anomaly", is the entity that controls Frisk and presumably Chara during most of the game. They are responsible for most of Frisk's actions and for the Genocide Route, which is owed to the being's own callous disregard for the life of those in the Underground, simply performing genocide not because they have to, but because they can.
When they appear in the Underground with Frisk, their own determination wakes up Chara and forces them to possess Frisk. The name chosen by the Player in the beginning of the game goes to Chara, though the child's story and motives remain unchanged. Here, they can chose which route they want Frisk to take.
In the True Pacifist Route, the Player takes actions according to Frisk's personality most of the time, which leads to the reveal of the latter's name, in the end. This implies this route best represents Frisk's true nature as a person without the Player pushing them in different directions. Although Asriel himself doesn't make mention of the Player, Flowey directly addresses them in the true ending's epilogue, begging them to not reset. Although he is powerless to stop them, he mentions that his memory will be lost as well, and he will lose his recent memories as Asriel and once again go back to his old, emotionless self. Despite this, his knows the Player has probably heard this hundreds of times before, and leaves them with one final farewell, referring to them as "Chara". This is one of the few events outside of the genocide route which hints to Chara's relation to the player and their Determination, as in resetting the world and tearing away everyone's happy ending, the Player is once again falling prey to their own callousness.
The Player is rarely alluded to during the neutral route, although it is left ambiguous to if Flowey is addressing the Player or Frisk in his neutral ending dialogue.
Unlike the other two endings, the genocide route ending revolves around the Player as a pivotal character. They are the one who forces Frisk all the way through the route, while also unknowingly feeding Chara with their own Determination. When Frisk reaches Sans, the skeleton notes that an anomaly has been appeared within the space-time continuum, causing timelines to sporadically jump around before being deleted entirely. Sans realizes that the heinous crimes committed have not been of Frisk's own volition, but instead merely a product of the Player's Determination to find out what happens next and the ever-growing influence of Chara. Knowing he cannot hope to beat a force beyond his own reality, Sans attempts to simply beat the Player/Chara over and over again (and as a last ditch effort, stand in a stalemate for all eternity), until they get bored and quit, erasing this timeline and starting a new one in which they will embark on a different path. However, ultimately he too falls to the Player's Determination.
At the very end of Genocide Route, Chara takes direct control of Frisk and murders Asgore and Flowey, not allowing the Player any input in the matter. The spirit then manifests in front of Frisk, addressing the Player directly. They mention how their Determination and SOUL wasn't theirs, but in fact the Player's, with Chara acting as merely an extension of themself. The Player was also the reason they were brought back into existence in the first place, along with being the one who showed them the reasons for their new existence. Chara will then proceed to offer the Player the opportunity to erase the world together, allowing the two of them to move onto the next and purge it, as well. No matter their answer, Chara will attack the screen and destroy the game itself.
Upon re-entering what used to be the game, the Player will find it empty. After 10 minutes, Chara will notice that the Player wants to go back to the world they destroyed. The demon child will call out the Player for thinking they were above consequences before then offering them a deal; The Player will give them something they want, and in return, Chara will restore the world. Should they accept, Chara will take The Player's SOUL before bringing the world back. Because of this, any pacifist ending acquired after this one will have the same result, allowing Chara to possess Frisk over and over again in order to wipe everyone else out as they prove their point that no one is above consequence.
Powers and Stats
Tier: At least 2-C, likely 2-B
Name: Unknown, Chara, The Player, The Anomaly
Classification: Space-Time anomaly originating from outside of the world
Powers and Abilities: Superhuman Physical Characteristics, Timeline Manipulation, Time Manipulation, Memory Manipulation, Data Manipulation, Non-Corporeality, Possession, Mind Control, Minor resistance to Memory Erasure
Lifting Strength: Unknown
Striking Strength: Unknown
Durability: Unknown (Has survived so far every action and Multiverse destruction in the game without ever being in danger)
Range: At least Low Multiversal, likely Multiversal
Standard Equipment: Frisk
Weaknesses: Can't directly interact with the Undertale world without an host like Frisk. Their host can rebel or perform actions on their own if their Determination is strong enough, such as Frisk attempting to access SAVEs during their fight with Asriel, or Chara overriding the Player's control and forcing Frisk to kill Asgore and Flowey.
- Reset: Resets the timeline
- True Reset: Resets the world, deleting everything which has ever happened, along with everyone's memories. Unlike the normal reset, the True Reset even wipes the memory of those who can remember information across multiple timelines. The only exception to this is Chara, and that is only if they are able to acquire the Player's SOUL.