One For All is the transferable Quirk that is possessed by its ninth and current host, Izuku Midoriya.

In the past, it was originally used by Yoichi Shigaraki, and later, its other previous hosts: Hikage Shinomori, Daigoro Banjo, En, Nana Shimura, Toshinori Yagi, and the other two users before them.

Long ago, All For One, a man with a Quirk that allows him to steal other people’s Quirks and transfer them to others, forced a Quirk on his seemingly Quirkless younger brother, Yoichi. This Quirk allowed him to stockpile power within his body. However, unbeknownst to either one of them, Yoichi already had a Quirk with no other power than that it could be transferred to another person. The transference Quirk and the power stockpiling Quirk merged to form One For All.