All For One

All For One is the most powerful and dangerous villain in My Hero Academia history, and the true mastermind behind the League of Villains. His Quirk, also called All For One, allows him to steal other people's Quirks and use them as his own, as well as forcibly give Quirks to others. He has lived for over a century by stealing longevity-granting Quirks, and he created the original One For All by forcing a stockpiling Quirk onto his seemingly Quirkless brother. After being defeated and imprisoned by All Might, he continued manipulating events through Tomura Shigaraki, whom he groomed as his successor and eventual vessel for his consciousness.