All might

Even as a Quirkless teenager, Toshinori Yagi possessed a strong sense of justice. He came up with the concept of "The Symbol Of Peace", to provide hope for citizens and alleviate their fears in the face of rising crime rates. He was greatly influenced by his One For All predecessor and mentor, Nana Shimura, and admired her as a mother figure. He was also mentored by Nana's best friend, Gran Torino, although he feared Gran Torino's violent sparring sessions. Nevertheless, he respected the older Pro-Hero.

In his public persona, All Might always sports a cheerful smile. He is a jovial, magnanimous, and courageous larger than life man, who presents himself as the ever-victorious Symbol Of Peace. All Might's exceptional achievements inspired an entire generation of heroes. Even the Hero-Killer Stain admires All Might as a true hero and evaluates other heroes using the Symbol Of Peace as the standard. In private, All Might becomes a more solemn individual. In his prime, he was notorious for being an extreme workaholic, ignoring the cautions of his sidekick, Sir Nighteye, and working non-stop up to 72 hours.

All Might is proud of his protege and successor, Izuku Midoriya, appreciating the boy's fearless commitment towards saving people. He also commends all students at U.A High for their courage and effort, reckoning them as true heroes. After losing his powers and retiring as a Pro-Hero, All Might dedicates himself to become a better teacher to all students, and does his best to mentor Izuku.

Despite his optimistic personality, All Might utterly loathes the supervillain, All For One. As a teenager, All Might was traumatized by the death of Nana Shimura at the hands of All For One. After becoming a Pro-Hero, All Might dedicated his efforts towards destroying All For One's criminal empire across Japan. He cannot comprehend nor tolerate All For One's crimes of exploiting people and ruining their lives. All Might is anguished upon learning that All For One's successor, Tomura Shigaraki is Nana Shimura's grandson.

In his true form, All Might becomes a more serious and focused person, although is still capable of showing his genuine smile and concern for others well-being, albeit not at his usual grandiose extent.

Regardless of what form he is in, All Might still embodies the ideals of a true hero with a good heart to match. Ever since he was young, he dreamed of becoming a symbol that others could rely on during harsh times, upon receiving his Quirk he would rise not only to become that symbol but to become a legend that would inspire countless others to become heroes and follow in his will. Even the notorious Hero Killer, Stain, regards All Might as a true hero and what every hero should be; selfless and willing to help others.

After his retirement, All Might dedicated the rest of his life to training Izuku, entrusting him with the information about the other One For All users and their Quirks.