Asgore is the King of all Monsters, ruler of the Underground. He is the ex-husband of Toriel, father of Asriel Dreemurr and the guardian of the first human. He is gentle at heart, being loved by his people and loving gardening, Golden Flower Tea and his ex-wife's Butterscoth Pie. However in a fit of anger, because of the death of his children, he promised to kill every human that fell down, take their souls and then destroy humanity, making his wife leave him, disgusted with his actions. However he doesn't want to do any of those things, and immediately regreted his actions, but had to keep his duty since that was the only thing giving his people hope in their underground prison. His duty with his people is killing him inside since that day, nowadays all he wants is just to see his wife and child again.
heres a ref of what he sounds like
https://www.youtube.com/watch?v=GC9xvg7xQ44