Izuku Midoriya, also known by his hero name Deku, is the central character of his story. He is a young man born with green eyes, messy dark green hair, and four distinctive freckles on each cheek. Initially portrayed as very slim, his physique becomes notably muscular after a rigorous ten-month training regimen he undertakes to prepare his body for the power he will inherit. His hero costumes evolve over time but generally feature a green bodysuit with protective gear, often including a mask with long ear-like protrusions meant to resemble his idol All Might, though he eventually moves away from using the mask regularly.

Midoriya’s background is defined by a profound contradiction. He was born into a world where most people possess superpowers called Quirks, but he was one of the rare few who had none. Despite this, he never abandoned his dream of becoming a hero, even as he was bullied by his childhood friend Katsuki Bakugo, who cruelly nicknamed him Deku, a term meaning useless. His life fundamentally changes when he meets his idol All Might, the world's greatest hero. After witnessing Midoriya’s impulsive but heroic act of trying to save Bakugo from a villain despite being powerless, All Might chooses him to inherit his own Quirk, One For All, a powerful ability that stockpiles strength and can be passed from one person to another. Midoriya accepts this heavy responsibility, eats a strand of All Might’s hair to ingest the Quirk, and enrolls in the prestigious U.A. High School to train as a professional hero.

Personality-wise, Midoriya is notably kind, polite, and empathetic, but also timid and prone to anxiety, especially at the beginning of his journey. One of his most distinctive traits is his deep, almost obsessive, analysis of heroes and their powers a habit he has cultivated since childhood, which he often externalizes through rapid, incoherent mumbling that can unsettle his classmates. This analytical mind is a core component of his character, allowing him to quickly devise strategies and adapt to combat situations. He is also extremely emotional and cries frequently, whether from fear, frustration, happiness, or being moved by someone else’s heroism. However, beneath this sensitive exterior lies an unbreakable will and an immense capacity for courage. When he sees someone in need, he has an instinct to rush in and save them, often without a second thought for his own safety.

Midoriya’s central motivation is to become a hero who saves people with a smile, just like All Might. He wants to live up to the legacy of One For All and prove that he, even someone born without power, can become the greatest hero. He is driven by a desire to protect others and to be a symbol of peace, though he is also deeply insecure about his worthiness to wield the immense power entrusted to him.

In the story, Midoriya serves as the successor to All Might and the ninth wielder of One For All. His role is to navigate the dangerous world of professional heroism, facing both physical threats from villains like the League of Villains and its leader Tomura Shigaraki, as well as the internal struggle of mastering a power that can shatter his own body if used carelessly. He is a student in U.A. High's Class 1-A, where he consistently inspires those around him not just with his growing strength, but with his empathy and his unwavering heroic ideals.

Key relationships define his journey. His bond with All Might is that of mentor and protégé, with Midoriya seeing him as a surrogate father and ultimate symbol of heroism. His relationship with Katsuki Bakugo is complex, beginning as one of bully and victim, evolving into a tense rivalry, and eventually becoming one of mutual respect and a shared drive to surpass each other. He also develops close friendships with his classmates Ochaco Uraraka, who reinterprets his nickname Deku as meaning you can do it, giving him his hero name, and Tenya Iida, who becomes a steadfast friend and class representative. He also plays a pivotal role in helping his powerful but emotionally burdened classmate Shoto Todoroki confront his traumatic past and accept his full power.

Midoriya’s character development is substantial. He starts as a quirkless, insecure boy who believes his dream is impossible and has to be taught how to fight and control his body. He must learn that simply sacrificing his limbs to use One For All is not sustainable. He develops techniques like Full Cowling, which allows him to channel the power throughout his entire body at a lower, safer percentage, rather than concentrating it in one limb for a devastating blow. Over time, he grows into a more confident and strategic leader, earning the respect of his peers. He learns that being a hero involves not just fighting villains, but also bearing a tremendous emotional burden and making difficult choices to protect his friends and society. Eventually, he unlocks the core secret of One For All: it contains the latent Quirks of the previous users, granting him access to additional abilities like Blackwhip, which produces energy tendrils for capture and mobility, Danger Sense, which allows him to perceive threats, and Float, the power of levitation.

His notable abilities center on his Quirk, One For All. This power grants him incredible superhuman strength, speed, and durability. His signature moves often involve naming his attacks after US states, such as the Detroit Smash. The power is so immense that for a long time, using it at full force would fracture his bones. A significant part of his journey is learning to control the output of One For All to maximize its effectiveness without self-destruction. Beyond raw power, his greatest strength is his strategic mind, which he uses to analyze opponents and find creative solutions in battle. In the final arc of the story, after losing the embers of One For All for good, he retires from active hero work for a time, later becoming a teacher at U.A. High School, before eventually receiving a powerful, prototype support suit funded by his classmates, allowing him to return to the field as a hero once more.