Toshinori Yagi also known as All Might , was the former No. 1 Pro Hero who bore the title of the world's Symbol of Peace. He teaches Foundational Hero Studies at U.A. High School. All Might was the eighth holder of the One For All Quirk after receiving it from Nana Shimura. He has since passed the torch to Izuku Midoriya, whom he is training to be his successor. After using up all the embers of One For All to defeat All For One, All Might retired and ended his era as the world's greatest hero. All Might was recognized as the greatest hero in the world. He was the "Symbol of Peace" and such a deterrent against crime that villains were largely discouraged by his presence in society, single-handedly bringing near-absolute stability throughout Japan, a stark contrast to the rest of the world. He was able to defeat All For One, infamously known as the world's most powerful villain, twice; a feat that all the previous wielders of One For All could not.
Despite winning however, All Might suffered a gruesome injury at the hands of All For One that limited his maximum power output going forward, gradually reducing his sheer might and how long he could use his power at all. Even after his Quirk's power was constrained by his injuries, All Might's strength and speed were unmatched. After he passed his Quirk onto Izuku, relying on the residual energy of One For All made his strength and time limit decrease more rapidly. Even so, All Might could still defeat villains on his own that groups of normal Pro Heroes struggled against. By pushing his power beyond its reasonable limits, All Might defeated Nomu, who was created specifically to kill him, with over 300 blows. Against Izuku and Katsuki, who are among Class 1-A's elites, he completely dominated them in their fight, even while wearing high-density weights. Forced to once again break the limiter placed on his Quirk, All Might defeated All For One by using up his remaining reserves of power. Even though he is unable to keep his hero form for more than a few seconds after his final battle with All For One, All Might still keeps a keen intuition and sharp reflexes, which helped him hone his skills as a hero ever since he acquired his powers. This is shown in his observations regarding Izuku's use of One For All, and the fact that he was capable of catching one of Mei Hatsume's "babies" coming in from behind with minimal effort in his true form. Despite his physique in his true form, he is actually quite physically able but isn't as efficient compared to when he is in his hero form. Usage of One For All requires the user to have strong muscles, as One For All is a lot to handle and could cause the user's body to be blown apart if they don't possess the necessary strength of body. Gran Torino said that All Might, in particular, had a strong body that allowed him to master One For All much faster than previous users. One For All Transferred to him from Nana Shimura, Toshinori's Quirk allowed him to stockpile an enormous amount of raw power, allowing him to significantly enhance all of his physical abilities to a superhuman level. This resulted in unbelievable levels of strength, speed, agility, and durability. All Might was so proficient with One For All that he was widely known as the world's most powerful person. However, most of the known feats he performed are after he'd been grievously injured by All For One, and after he started the process of transferring One For All to Izuku, so the fullest extent of his abilities are mostly unknown.