Truly evil characters able to be good?

Hello, quite new here. (Never talked with other people who are into writing so sorry if I ask stupid stuff or something that has been talked about too many times here).

So I began to wonder about characters in fantasy/supernatural stories, who are written as evil, but they also have this genuinly nice side to them. But is it really believable that someone who murders and torturers and causes destruction upon innocents has a side to them that can care about someone? Even love. Does it really make sense? How can a character who does such despicable things be nice and caring towards someone... or is this just one of those fictional things that ger accepted because it's just fantasy and not reality. Thoughts?