Yoichi Shigaraki, was the younger brother of All For One, as well as the first user, progenitor of the One For All Quirk

Quirks One For All forcibly implanted a power stockpiling Quirk within him, it merged with his own Quirk, which had no other power than that it could be transferred to someone else, creating One For All his sickly state, he was unable to make good use of the stockpiling power and instead decided to pass it on to other people in hopes that his new Quirk would get stronger over time.