most people like either sans or toriel the most
Sans
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Rusty
No, unfortunately. He would be creepy if he was real so...thank god he is not.
Frisk is the name of the character you play. The name you are asked to enter at the beginning ('The Fallen Human') is actually the name for an important character in the game's background.
Probably Charlie...
She liked developing the character of Bella the best
I guess that's up to you
Undertale was created by Toby Fox, a game developer for the Mother series. You can actually find him in Earthbound as a dog in the shop in Onett. After Undertale, he later went on to create Deltarune Chapter One. Toby Fox's true identity is yet to be fully revealed.
A lot
Of course it is Harry, for he is the chosen one and is the main deal of the story.
Simon (of "Simon in the Land of Chalk Drawings") is a cartoon character of a school boy who liked to doodle in chalk.