In his empowered form, Toshinori is a very large man with an equally muscular and well-defined physique, his design resembling a typical western comic book superhero. He has short blond hair, swept backwards, with two distinct tufts that stick up above his head, leaning slightly to each side, which often casts a dark shadow over his face, hiding everything but his bright blue eyes.
Toshinori's Golden Age hero costume consisted of a skin-tight blue bodysuit decorated with a red symbol that somewhat resembles a "Y", designed with a white diamond at its center, with white lines connected to it that trace from his chest to his back shoulders, the lines trimmed with the aforementioned red symbol. The symbol appeared to have wings on the side that ran from the atop his torso before ending around his back, over which was a similar red and white design absent of the white diamond. Large white patches lined with red covered each side of his hips before ending at his lower thighs, and he wore a gold belt that had a silver buckle with red eyes. His forearm sleeves were colored in gold that each had white lines covered in blue accents over his wrists, and had spiked fins on the sides of his arms, his feet were covered in shin-length gold boots trimmed with white and red accents.
In his "true form", after sustaining permanent damage from All for One, Toshinori's declining health reduced him to a very skinny man with sharp, angular features and long limbs, his neck long and his eyebrows absent. He possesses a large scar that covers most of the left side of his chest, and it is not uncommon for him to spout blood from his mouth when excited or surprised. He typically wears baggy clothing to accommodate the change in body mass between forms, but after the end of Toshinori's tenure as a hero, he starts wearing clothes that fit him in his true form, as he no longer needs big clothes that fit his muscle form.
In his early career, Toshinori was a lean but fit young man. In his empowered form, his facial features were noticeably softer. In both his normal and empowered form, he did not have shadowed eyes on his face, completely showing his white sclerae while retaining the deep blue irises of his eyes, possibly showing how he was not a shell of his former self.
All Might's hero persona appears to be derived from comic book superhero stereotypes: colorful and filled with dramatic flair. Always sporting a giant smile, All Might shows a bright, borderline obnoxious, can-do attitude that is said to inspire others as well as help them feel safe and hopeful. He 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, however, he becomes less energetic and more serious, generally taking a milder stance so as to not attract much attention to himself, in direct contrast to the grandiosity of his hero identity. 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 too. 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. Indeed, after obtaining One For All from his master, Nana Shimura, as well as inheriting her habit of smiling at all times, All Might rose to become not only a hero, but a legend, no thanks to his seemingly endless competency and charisma. No matter who or what he faced, All Might would stand up triumphantly in the end every time, inspiring the world and sending fear to the hearts of villainseverywhere.
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 Midoriya, in a brave attempt to save a classmate from a villain attack despite his lack of power, rekindled his heroic spirit and taught him that something can always be done to fight injustice.
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, even though he is still outsmarted by his students sometimes. He struggles both as a teacher for Class 1-A and mentor to Izuku due to his lack of teaching experience, requiring scripts in order to convey his lessons. All Might's fellow teacher, Shota Aizawa, calls him an idiot on occasion because of this while Gran Torino believes that all his strength and fame has not translated well into instructing or training others, especially as he never struggled to learn about One For All in the first place.
All Might always prioritizes the lives of others over his own, considering them his responsibility be them civilians or other heroes. Still, All Might is deeply aware that saving everybody in the world is an impossible task, but he always does his best or even beyond that to minimize as many casualties as possible. 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.
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" (少年, Shonen?) to the surname of his students whenever he is speaking out loud or thinking to himself (ex. "Young Midoriya").
