Dabi

The Birth of Dabi
Toya miraculously survived, although he remained in a coma for years under the care of others. When he awoke and secretly returned home, hoping to rebuild their relationship, he saw his father continuing the same harsh abuse against young Shoto. Seeing that nothing had changed and that he had been easily "replaced," Toya's mind broke.
He abandoned his real name and adopted the pseudonym Dabi. He used skin grafts and surgical staples to hold together the burned skin of his body and began operating as an assassin in the shadows.
League of Villains and Revenge
Inspired by the ideology of the Hero Killer, Stain (who preached the elimination of false and hypocritical heroes), Dabi joined the League of Villains led by Tomura Shigaraki. However, his personal goal was never the League's cause, but rather to orchestrate Endeavor's downfall and public humiliation.
During the Paranormal Liberation War, Dabi revealed his true identity as Toya Todoroki to the entire world via television broadcast. He exposed Endeavor's domestic abuse, destroying society's trust in the new "Number One Hero" and completely destabilizing the hero system in Japan.

Dabi is one of the most iconic and complex villains in My Hero Academia. His story is entirely marked by rejection, obsession, and a visceral desire to destroy his own father's reputation.
The Origin: Toya Todoroki
Dabi's real name is Toya Todoroki, the eldest son of Enji Todoroki (the pro hero Endeavor) and Rei Himura. Enji married Rei solely to merge their Quirks (Fire and Ice) and create a son capable of surpassing the number one hero, All Might.
When Toya was born, he demonstrated flames even hotter and more powerful than Endeavor's. His father saw in the boy the fulfillment of his greatest dream and placed all his ambition upon him, fueling in the boy the obsession to become a great hero.
Rejection and Collapse
The problem arose in childhood: Toya inherited Endeavor's fire powers, but his mother's resistance to cold. This meant that every time he used his flames, his own body would be severely burned. Realizing the danger and considering Toya a technical "flaw" for his goal, Endeavor abruptly stopped training him and focused on raising other children until the birth of Shoto, the "perfect" boy who inherited both fire and ice.
Rejected and desperate for his father's attention, Toya continued to train in secret in the mountains, ignoring the pain of his burns and making his flames even hotter—at which point his fire changed to blue. At age 13, he arranged to show the evolution of his power to Endeavor at Sekoto Peak, but his father did not appear. Emotionally devastated, Toya lost control of his flames and ended up causing a catastrophic forest fire. He was presumed dead, with only a bone fragment remaining at the scene.