Frisk
Frisk is the true identity of the main character, should player take the correct actions in game. They could be considered one of the most powerful individuals in the game as they posses the power to SAVE and to Reset their progress.
Frisk only appears in the True Pacifist route, though at first everyone will believe them to be Chara. While Frisk's personality is ultimately determined by the player's choices, it can be deduced that Frisk truly is a pacifist as they never wish to harm those they come across even when that individual wishes to fight or otherwise kill. Furthermore, Frisk appears to be a rather selfless and forgiving individual as they are willing to help out some of the monsters with their troubles even after being attacked. When visiting Undyne to befriend her, she'll say that Frisk is a lot like Asgore; "a wimpy loser with a big heart." In the final boss fight of the True Pacifist route, even more of Frisk's power and personality can be seen when they use the power of SAVE to rescue their friends from Asriel's influence. After Ariel calms down, Frisk's true identity will be revealed and Asriel will use their power to ensure that everyone will know as well. Should the player choose to explore the Underground before leaving for the Surface, interacting with the residents will reveal that while they do recognize Frisk as "Frisk the human" they still remember the deeds they preformed beforehand, thanking them and apologizing for their prejudice towards humans. Should the player return all the way back to the beginning area to speak with Asriel, he note that he's surprised at how he tried to project Chara onto Frisk as the two had nothing in common aside from their "taste in fashion." Further more, Asriel will state that Frisk is the friend that he should have had back then, considering what kind of person they are compared to Chara. Once Frisk leaves for the surface with their friends, Asgore will ask Frisk if they could act as an ambassador between Monsters and Humans only for everyone to leave Frisk alone with Toriel. Should the player chose for Frisk to stay with Toriel, a cutscene will play after the end credits showing Frisk asleep in bed as Troiel leaves them a piece of pie for when they wake up.