Undertale Frisk is the character who is a human child and the main protagonist in Undertale. It is for him that the player will play throughout the entire game.
According to the plot of the game, the child accidentally finds himself in a world where monsters live, now he needs to go on a long and distant adventure in order to get back. On his way, he will meet many different monsters. Someone will turn out to be a friend, and someone will have to be killed. What happens to them is up to the player to decide. So, depending on the ending that the player goes to in the final, there will be either friends that the player made for himself during the game, or he will kill everyone. In addition, the very reaction of monsters to the player will also depend on which ending the player is going to.
Speaking of the neutral path in the game Undertale, we can say that it has several additional endings that differ depending on who was killed by the player. Someone wants to take revenge, someone will feel upset and depressed, and someone will become the new king or queen of the Underground.
If the player does not want to kill anyone and wants to be a pacifist, then firstly only in this case the player will find out the real name of the main protagonist, namely Frisk. In the finale, the monsters, along with the human child, leave the Underground and come to the surface.
The path of blood and murder which the player can get by playing the ending called Genocide is also quite interesting, as you can learn about Chara, who is the first person to enter the Underground and Asriel’s friendship with her. Also, here you can learn a lot of interesting things from the main antagonist Flowey, who trusts the main protagonist very much, as he reminds him of Chara, his friend.