Unexpected pure of heart?

I’m not sure if this is a movie, tv show, video game, anime, or whatever-I just found myself suddenly thinking about it after a long time.  I only remember that there was this big deal made about someone being pure of heart.  Maybe that person was needed to do something or was immune to something, I don’t know.  But I do recall that the person who was pure of heart was someone unexpected, like a jerky character.  I don’t know if it was mentioned, but I remember at least theorizing that this person was the most pure because, while a jerk, they were honest. They didn’t lie about who they were.  Actually, it might not even have been a pure of heart thing, but something similar?  Like, the person who was the least selfish or something?