Asriel Undertale is essentially the same Flowey that the player meets at the beginning of the game. He talks about his motto, which sounds like “Kill or be killed”. He is going to try to kill the player, but the main protagonist will be saved.
His parents are the King and Queen of the Underground named Asgore and Toriel. The story begins long before Frisk got into the Underground. It was then that the human child Chara, the player enters the name of the child at the beginning, falls into the world of monsters for the first time, and is soon adopted by the royal family of the world where monsters live.
The prince quickly became friends with the girl, and they played a lot and spent time together. They had a lot of funny memories. But, soon due to illness, his friend and also part-time half-sister dies, and later he himself. Deciding to take Chara to her home village, as she wanted to see her favorite flowers before dying. People think that he killed the child, and then they start attacking him. As a result, he returns to the world of monsters and dies due to injuries.
Throughout the passage of the game, the player can learn a lot of interesting things about what happened before this and the details of the friendship between the prince and the human child. Also, until the end of the game, he does not recognize Frisk as the main protagonist, since until the end he imagines that this is Chara.
Speaking about the present tense, it can be noted that you have the opportunity to meet with it in its usual form if you go to the Pacifist ending. You have the opportunity to see him as an adult and have a battle with him.