All Might's hero persona appears to be derived from comic book superhero stereotypes: exuberant and filled with dramatic flair. He always protects and saves innocents, with a huge smile. The habit of smiling was ingrained to him by his mentor, Nana Shimura, who believed that the ones who smile are the ones who are the strongest. Though he can be annoying at times, All Might is extremely friendly and amicable due to his popularity and years in the spotlight, always taking his time to interact with fans.

Once All Might reverts to his true form, he becomes reserved and solemn, avoiding attention in direct contrast to the grandiosity of his hero identity. While he's an optimist, he still ensures his goals are grounded in reality. When a Quirkless Izuku tells him about his goal of becoming a hero, All Might praises him for having a dream, but reminds him to stay realistic and suggests he enter another profession that helps people. He considered the harsh words necessary to save the boy from long-term frustration. In this form, he frequently vomits blood as an indicator of his fragile health, although it might happen if he gets surprised or amused enough. Two personality traits that seem to be always present on him, regardless of which form All Might is currently taking, are his optimism and oafishness.