Though born without a Quirk, he manages to catch the attention of the legendary hero All Might due to his innate heroism and has since become his close pupil as well as a student in Class 1-A at U.A. High School. All Might passed on his Quirk to Izuku, making him the ninth holder of One For All. Izuku is a very timid, helpful, and polite boy, frequently overreacting to abnormal situations with exaggerated expressions. Due to being bullied for lacking a Quirk, he is initially portrayed as insecure, more reserved, and non-expressive. These traits are especially present around Katsuki Bakugo, who constantly subdued him for his aspirations to be a hero. However, after being accepted into U.A. High School, making new friends, and facing Katsuki during the Battle Trial Arc, Midoriya gradually turned into a more confident and brave person, eventually developing leadership skills.
Toshinori Yagi, most commonly known by his hero name, All Might, is the tritagonist of My Hero Academia. All Might is the former No. 1 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 grooming 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'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.
Katsuki Bakugo, also known as Kacchanby his childhood friends, is a student in Class 1-A at U.A. High School, training to become a Pro Hero. He is crude, arrogant, and aggressive person, especially at the beginning of the series. Katsuki tends to come off as an anti-hero, if not downright villainous for those not familiar with him. This problematic behavior goes all the way back to his early childhood days when he was known to bully a young, Quirkless Izuku Midoriya. However, after being accepted into U.A. High School and experiencing several personal defeats, one of them even coming from Izuku, Katsuki has gradually changed into a less antagonistic person, albeit still retaining a lot of his unpleasant traits.
Tenya Iida, also known as Ingenium, is the class representative of Class 1-A at U.A. High School, and is training there to become a Pro Hero. He is one of the main protagonists of My Hero Academia. Tenya may look severe, but he's actually a very straightforward, earnest, intelligent and noble person. He tends to take everything very seriously, and because of this, he has a habit of jumping to conclusions, then enthusiastically speaking or acting based on said conclusions. For example, after assuming that Izuku Midoriya had figured out the true nature of the U.A. Entrance Exam, Tenya acknowledged him as a worthy peer and has since held him in high esteem. All this enthusiasm leads Tenya to be hyperactive and intense, having some involuntary body tics such as moving his arms around in strange patterns and sometimes twitching his own body uncontrollably.