Garou is an eighteen-year-old former disciple of the martial arts master Bang, who is also an S-Class hero known as Silverfang. Possessing immense natural talent, Garou was once Bang’s most promising student before he turned against the dojo, severely injuring all of his fellow students and forcing his master to expel him. Following his expulsion, Garou embarks on a self-appointed crusade to hunt down heroes, earning him the titles Hero Hunter and Human Monster.

His motivations stem from deeply personal experiences during childhood. As a boy, he was often ostracized and forced to play the role of the monster in games by other children, who would then physically bully him while receiving no reprimand from adults. This was compounded by his frustration with a television show in which heroes always defeated the monsters, a narrative he found fundamentally unfair as he sympathized with the villains who struggled and lost regardless of their efforts. As a result, Garou developed a deep-seated resentment toward what he perceives as the world's unfairness and the hypocritical, self-righteous nature of society's proclaimed justice. His primary goal is to become Absolute Evil, a being so terrifying and powerful that he creates a twisted form of world peace by uniting humanity against him, thereby toppling the existing heroic order.

Garou is characterized by a rebellious and arrogant personality, driven by a singular obsession with his own strength and ideology. Despite his claims of becoming a monster, he possesses a strong, albeit warped, sense of his own principles. He refuses to kill, instead seeking to break the spirits and bodies of heroes to prove the weakness of their cause. In a surprising contradiction to his villainous persona, he exhibits a protective instinct toward children, particularly a young boy named Tareo, whom he sees as a reflection of his own bullied childhood. This inherent decency often leads him to take actions that are accidentally heroic, a fact that his opponent Saitama later points out during their final confrontation.

Throughout the story, Garou serves as the central antagonist of the Human Monster Saga. His role is to systematically challenge the Hero Association, starting with lower-ranked heroes and progressing to S-Class fighters, pushing the established order to its breaking point. His character arc is one of violent evolution and eventual disillusionment. After being taken in by the Monster Association, he is subjected to brutal trials that force him to evolve rapidly, culminating in a complete monster-like transformation. He successfully defeats numerous S-Class heroes, coming closer than almost any other villain to achieving his goal. However, his crusade ends when he meets Saitama, who effortlessly defeats him and forces him to confront the childish and performative nature of his rampage, revealing that Garou's true desire was not to be a monster but to be a hero.

His key relationships define his path. His former master, Bang, seeks to stop him out of a sense of responsibility and lingering care, creating a deeply conflicted dynamic. He develops a fierce rivalry with the S-Class hero Metal Bat, whose relentless fighting spirit earns his grudging respect. Other significant encounters include a one-sided defeat against the beast-like hero Watchdog Man, a strategic analysis of the powerful hero King that ends in failure due to Saitama, and a battle against Superalloy Darkshine that breaks the latter's spirit. The boy Tareo serves as his moral anchor, and his interactions with the Monster Association's leaders, Psykos and Orochi, highlight his rejection of their mindless savagery in favor of his own intellectualized version of evil. Above all, his relationship with Saitama serves as the final judgment on his ideals, proving that his strength is insufficient and his philosophy is a hollow rationalization for a childhood grudge.

Notably, Garou is not a monster but a human with extraordinary martial arts abilities. He is a master of the Water Stream Rock Smashing Fist, a technique that uses the flow of an opponent's power to deflect and redirect their attacks. His true strength lies in his genius-level adaptability and growth; he can analyze, copy, and counter an opponent's fighting style after witnessing it only once, and he has the ability to break his own limits in the face of death, growing exponentially stronger during combat. As he undergoes his monsterization process, he gains fearsome physical transformations that increase his power, speed, and durability, eventually reaching a level that surpasses nearly every hero in the association, with a disaster level rated as Dragon or above. He also possesses high resistance to pain and injury, a strong will that resists psychic control, and the ability to create afterimages through sheer speed.