Baki Hanma is the central protagonist of his namesake series, a teenage martial artist of immense talent driven by a singular, all-consuming goal. He is the son of Yujiro Hanma, a figure known as the strongest creature on earth, and Emi Akezawa. From early childhood, Baki was subjected to a rigorous training regimen, funded by his mother and designed to forge him into a warrior capable of standing against his own father. By the age of thirteen, he abandoned formal training methods in favor of his own brutal and unconventional path, seeking to follow in his father's footsteps.

Baki's personality is defined by a complex duality. Outside of combat, he often displays a laid-back, almost detached demeanor, showing little interest in material wealth or ordinary social life. However, this calm exterior masks a fierce and relentless warrior spirit. He is driven by an intense, almost obsessive desire to surpass his father, a motivation that was crystallized and darkened by the trauma of witnessing Yujiro kill his mother, Emi, while she tried to protect him. This event transformed his quest from a desire to prove himself into a deep-seated need for vengeance and self-definition. Unlike his father, who revels in brutality and dominance, Baki fights with a sense of honor and fairness. He rarely seeks to kill his opponents, respects strength in others, and will go to great lengths to protect those he cares about, particularly his girlfriend, Kozue Matsumoto.

Throughout the story, Baki's primary role is that of a challenger, constantly seeking stronger opponents to test and hone his abilities. His journey takes him from the underground fighting arena beneath the Tokyo Dome, where he becomes champion, to encounters with legendary warriors from around the world. His key relationships are central to his development. His bond with his father, Yujiro, is the story's core, a volatile mix of hatred, respect, and a twisted familial connection. Baki also has a complex rivalry with his half-brother, Jack Hanma, whom he defeats in the finals of the Maximum Tournament. The support and stability offered by Kozue Matsumoto provide a crucial emotional anchor, offering a contrast to the violence that defines his life.

Over the course of the series, Baki undergoes significant character development. He evolves from a hot-headed and vengeful youth into a more reserved and strategically-minded martial artist. His initial drive for revenge matures into a more nuanced understanding of strength, seeing it not just as a means to dominate but as a form of self-expression and a path to personal transcendence. This evolution culminates in the climactic father-son battle, where he finally earns Yujiro's acknowledgment, not as an equal, but as the strongest boy in the world.

Baki's notable abilities are as extraordinary as his willpower. He practices a self-styled "Total Fighting" style, an effective blend of techniques absorbed from numerous martial arts. He is a genius of adaptation, capable of replicating complex techniques after seeing them only once. A hallmark of his training is an advanced form of mental simulation or "shadowboxing" so vivid it allows him to pre-visualize entire fights and learn his opponents' weaknesses before engaging them. He possesses the Hanma bloodline trait known as the "Demon Back," where his back muscles form a demonic face, temporarily doubling his physical strength, speed, and durability. Other signature techniques include the "Cockroach Dash," an explosive, multi-directional dash that mimics the initial burst of a cockroach, and the "Whip Strike," a whip-like punch designed to inflict maximum surface pain. Baki's body is an instrument of peak performance, boasting muscle density and durability that surpass Olympic-level athletes, allowing him to withstand incredible punishment and recover at an astonishing rate during combat.