Enji Todoroki, known professionally as the Flame Hero Endeavor, was originally the second-highest ranked professional hero in Japan, a position he held while driven by an intense and all-consuming rivalry with the top hero, All Might. This competitive drive, rooted in a personal conviction to become the strongest, was his primary motivation for decades. A pivotal moment in his childhood, witnessing his own father die during a rescue attempt, had ignited his original desire to become a hero, but this noble origin was eventually overshadowed by his fixation on surpassing the seemingly insurmountable Symbol of Peace.

Endeavor's personality is complex, marked initially by pride, a volatile temper, and a professional demeanor that many found callous or indifferent. His public persona was that of an effective but harsh hero who prioritized results over charisma. In his private life, this ambition curdled into an abusive obsession. Convinced that his own Quirk, Hellflame, had a critical weakness—overheating his body and limiting his stamina—he concluded he could never defeat All Might on his own. To solve this, he orchestrated a Quirk marriage with Rei Himura, a woman possessing a powerful ice Quirk, with the explicit goal of breeding a child who would inherit both abilities and one day fulfill his dream of surpassing All Might. This quest for a perfect successor led to the systematic abuse and neglect of his family. He subjected his youngest son, Shoto, who inherited the desired combination of fire and ice, to brutal, isolated training from the age of five, while largely ignoring his other children, Fuyumi and Natsuo, as failures. His treatment of his wife, Rei, was a primary cause of her mental breakdown, which culminated in her scarring Shoto's face and her subsequent institutionalization. His eldest son, Toya, was initially trained as a successor, but was eventually discouraged due to his body's incompatibility with his powerful fire Quirk; Toya's subsequent secret training led to his apparent death, a tragedy for which Endeavor bears significant responsibility.

However, Endeavor undergoes a profound transformation following All Might's forced retirement. He ascends to the number one hero position by default, an achievement that brings him no satisfaction and forces him to confront the hollowness of his lifelong goal. This precipitates a crisis of conscience, and he begins a long and difficult path of atonement. He seeks counsel from All Might on how to be a worthy symbol, starts visiting Rei in the hospital, attempts to reconcile with his children (though Shoto and Natsuo remain cold and resentful), and comes to view his role as a hero not as a way to claim glory, but as a means to make amends for his past actions. His development is most starkly tested when he learns that Toya survived and has become the villain Dabi, who publicly broadcasts Endeavor's history of abuse to the nation. Confronted with the catastrophic consequences of his past, Endeavor does not make excuses but instead accepts full responsibility and commits himself to atone for his sins, even as his career and body are broken in the final battles against All For One and Dabi.

Within the story's narrative, Endeavor serves as a complex counterpoint to All Might. While All Might represents the idealistic, natural-born symbol of peace, Endeavor embodies a darker, more human side of heroism: a figure who achieved his position through relentless, often unethical effort and is then forced to live with the fallout. His key relationships are primarily defined by the family he destroyed and now seeks to heal, including his wife Rei, his estranged sons Shoto and Natsuo, his daughter Fuyumi who desperately wants reconciliation, and his archenemy Dabi, who is his own son Toya. His relationship with the young heroes he mentors, including Shoto, Izuku Midoriya, and Katsuki Bakugo, shows him as a surprisingly effective if harsh teacher, capable of imparting crucial practical skills and combat intelligence.

Notable abilities stem from his Quirk, Hellflame, which allows him to generate and manipulate enormous amounts of intense fire. He possesses exceptional control over his flames, able to shape them into concentrated beams, whips, projectiles, and even use them for jet propulsion to achieve flight. His signature techniques include Flashfire Fist, which raises his flames to their highest temperature; Hell Spider, which shoots out thin blades of fire; and his ultimate move, Prominence Burn, a massive, concentrated blast of flames powerful enough to vaporize a High-End Nomu. A significant weakness of his Quirk is that prolonged or extreme use causes his body to overheat, reducing his stamina and physical function. To compensate, Endeavor relies on immense physical strength, superhuman durability, keen analytical intellect, and an indomitable will that allows him to push past his limits, a trait that truly earns his hero name.