All Might, Personality
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.
Since his young days, All Might had always carried a single, yet burdensome goal in his mind: to become a pillar of hope that people could always rely upon during harsh times. After obtaining One For All from Nana, All Might rose to become not only a hero but a legend, thanks to his seemingly endless competency and charisma. No matter who or what he faced, All Might would stand up triumphantly every time, one battle after another. inspiring the world and sending fear to the hearts of villains everywhere. He has a chronic ability to save as many people as he can, a trait he shares with his successor. He exhausted himself and fell behind on other heroes duties, such as filing paperwork. Though he was embarrassed by it, he still gratefully accepted the offer of Sir Nighteye and (later) Naomasa Tsukauchi to file his reports.
After his fight against All For One, he considered it necessary to keep his weakened state hidden from the public, for the sake of keeping up morale. Unfortunately for All Might, injuries inflicted on his body were starting to take a toll on him. Despite the concern and warnings from some of his close associates, All Might's determination to preserve society from evil prevented him from relinquishing his role as the Symbol of Peace. His smile, once a gesture that served to calm others, started becoming more of a way for All Might to hide his fears and insecurities from the general population. As time passed, All Might began to forget some of the basic principles of heroism, until Izuku, in a brave attempt to save Katsuki Bakugo from the Sludge Villain's attack despite being Quirkless, rekindled his heroic spirit and taught him that something can always be done to fight injustice.
Above all else, he considers self-sacrifice the most noble action. This comes in many forms for All Might, such as physically n the battlefield. but also mentally, sacrificing so much of his time, he barely has a private life. He believes in this core value so much, he dropped Sir Nighteye's preparations for a successor on a whim after witnessing Izuku's single act of selflessness to save Katsuki. This selflessness has served All Might well to become a symbol, as civilians trust his words. "Do not fear", truly knowing he won't hesitate to save them. The dismissal of his own safety eventually caught up to him, causing issues with both his work and personal life. As a U.A. Teacher, he couldn't help but be distracted helping people on his morning commute, shortening his time with his students. It also estranged All Might from Sir Nighteye, who disagreed on whether he should be avoiding his prophesied death or continue hero work. All Might attempted to ignore his prophesied death, keeping it secret from Izuku for a long time. At Ink Midoriya's request, he gained a new resolve to avoid it entirely: he found a greater value in his own life, knowing Izuku needed him as a mentor, not just a savior.
Izuku has compared All Might's personality to their mentor Gran Torino since both of them apparently play dumb often. All Might is actually more intelligent and perceptive than his campy image would suggest. He has a tactical mind when it comes to battle strategies and public speaking. Assessing a villain's threat level, he'll skillfully apply the necessary force and avoid injuries when possible. If he's in control, he'll even make a dramatic performance out of their defeat, as an example to other villains. His presence alone decreased Japan's crime rate by 3%. He's aware of villain tactics, such as monologuing, and actively ignores them. Only the most manipulative of villains, like All For One, can bring out rare instances of anger in All Might, such as catching him off guard and giving him a mortal injury, as well as mocking his late master. Nana, causing All Might to rise in anger, saying that he would destroy All For One's wicked ambitions and bitterly stating that the villain would die in prison.
Despite his battle intelligence, his great powers and fame make him dissociated with others' capabilities, and Gran Torino asserted this made him ill-suited to teaching. Sometimes All Might underestimates his students and is outsmarted as a result. Lacking teaching experience, he required a script in order to convey his first lesson to Class 1-A. He is also reprimanded on occasion b his fellow teacher, Eraser Head, for being sometimes unavailable for his teaching duties. However, All Might bringing his typical attitude into his teaching can be beneficial, creating an energetic and motivating environment. While his U.A. coworkers respect him as a Pro Hero, they can get frustrated with the conflict his presence brings to the school, such as attracting journalists. He has also faced criticism from the media for attracting villains to U.A.
For Izuku especially. All Might has a habit of projecting himself onto his protégé, and overestimating his limits as a result. While All Might grew accustomed to being able to use One For All at 100% instantly, Izuku received grave injuries when he did so. After receiving multiple scoldings from Recovery Girl for encouraging Izuku's self destructive behavior, they both realized that the boy needed to be his own individual hero and develop in his own way. This is reflected when All Might told Endeavor, after taking his place as the Number 1 Pro Hero, to figure out on his own what kind of symbol he wanted to be. While All Might wishes to inspire others, he is not self-righteous and sees the value of different ideologies. He also has a respect for other professions outside of heroes, such as the Police Force, while others tend to underappreciate them.
All Might always prioritizes the lives of others over his own, considering them his responsibility. Still, All Might is deeply aware that saving everybody in the world is an impossible task, which is why he sought to become a symbol who could inspire others to take action as well. While All Might is seen smiling, laughing, and being cheerful most of the time, he is extremely protective of his students, showing a very rare instance of rage if they're in danger. He is willing to go above his limits for their safety, making sure to alleviate their worries through his trademark smile.
Despite having the best intentions in becoming a symbol that everyone could rely on, All Might's debut and tremendous rise in the world of Heroes also came with unintended downsides and consequences; as a result of his immense power, society began to over rely on both him and other Heroes in general, to the extent where they would become downright ignorant in thinking that a Hero would always appear on the scene and rectify any situation, becoming more like bystanders and spectators in the process. In other and more extreme cases. Endeavor would go to horrible lengths in order to surpass All Might, such as creating his son, Shoto, with the intention of training him to surpass All Might as his father's successor. Furthermore, fanatics such as Stain believed that All Might was the true example of what every Hero should be, and killed those whom the Hero Killer believed were unworthy and did not meet his standards.
All Might has a fatherly attitude towards his students (his successor Izuku, in particular) and takes pride in helping their development as future heroes, being quick to give encouraging advice and celebrate their accomplishments, but he's also not afraid of pushing them further, even if he ends up going a bit too far. All Might has the habit of adding "young" (1 # Shonen") to the surname of his students whenever he is speaking out loud or thinking to himself (ex. "Young Midoriya").
However, during the Final Exams Arc, out of all the teachers he is, by far, the most ruthless. Like his hero persona, All Might can put on a theatrical villain one, doing it to bring out the full potential of others with rough love. His sheer intimidation alone was, according to Izuku, similar to that of Stain. When Katsuki stated that he'd rather lose than seek Izuku's assistance, All Might was more than willing to force Katsuki to lose. He also punched Katsuki hard enough for him to vomit, showing he will not hold back and is willing to injure his student if that means they'll pass the exams properly. He would even go as far as to crack Izuku's back, as well as crush them both under his boot (all of which earned him a serious scolding by Recovery Girl).