All For One is a major antagonist in Boku no Hero Academia and one of the most powerful and feared villains in the series. He is the mastermind behind many criminal schemes and the original wielder of the All For One Quirk, which allows him to steal and use others' Quirks. As the symbolic opposite of All Might, he plays a central role in shaping the conflict between heroes and villains, influencing younger antagonists and threatening society from the shadows.