The character known as Black Jack is the central figure of his namesake series, a genius surgeon whose real name is Kurō Hazama. His most distinctive features are a direct result of a traumatic childhood incident. When he was a young boy, an explosion, often depicted as a landmine on a beach, killed his mother and left his own body nearly torn to pieces. He was saved by a miraculous operation performed by Dr. Jōtarō Honma. The aftermath of this event left his body covered in surgical scars, most prominently a long one across his face. The stress caused a portion of his hair to turn permanently white, while the skin on one side of his face is a darker shade due to a graft donated by a male friend, which he refuses to alter out of respect for that friendship.

Marked forever by this experience, Black Jack became a surgeon of unparalleled skill, though he operates without a medical license. This decision stems from a past insubordination where he performed an unauthorized but life-saving surgery on a lover, leading to his license being revoked and his subsequent rejection of what he sees as a corrupt and bureaucratic medical establishment. He exists as a shadowy figure, often seen wearing a long black cape, and he travels the world in his black car, taking on cases that other doctors have deemed hopeless.

On the surface, Black Jack presents himself as a cold, anti-social medical mercenary. He is infamous for charging his patients astronomically high fees, sometimes demanding sums in the millions or billions of yen, which has earned him a reputation for greed. However, this is a carefully cultivated facade. He operates under a complex and principled personal code. While he always establishes a patient's ability to pay beforehand, he will often waive his fee entirely for those who are poor or who move him with their story of suffering. He also frequently gives the bulk of his earnings to charity, using the money to fund environmental conservation or pay for other doctors' surgeries. He treats patients indiscriminately, from common folk to powerful yakuza bosses and even supernatural beings, but his fees are often scaled to the wealth of the patient. He might attach non-monetary conditions to his services for a rich patient, such as demanding they stop polluting the environment or leave their victims alone.

His role in the story is that of a wandering problem-solver, a force of nature who cuts through the ethical and physical complications of terminal illness and miraculous recovery. He is driven not by wealth, but by a deep-seated desire to honor the ideals of medicine that Dr. Honma embodied and to prove his own mastery over death. He learns harsh lessons about the limits of his own power, coming to terms with the fact that even he cannot always defy the forces of nature.

Key relationships shape his life significantly. He lives with his adoptive daughter, Pinoko, a sentient teratoid cystoma he extracted from a patient and placed in a synthetic body. He acts as a gruff but deeply caring father figure to her. He holds a profound debt of gratitude to Dr. Honma, the man who saved his life. He also has a notable rivalry with Dr. Kiriko, a fellow unlicensed physician who advocates for euthanasia as a merciful end to suffering, a philosophy that clashes directly with Black Jack's dedication to saving lives at all costs.

Throughout his journey, Black Jack shows subtle but significant development. He begins as a figure consumed by rage and a desire for revenge against those responsible for his mother's death. Over time, he softens, primarily through his relationship with Pinoko, and learns to channel his anger into his work, becoming more of a principled outsider than a purely vengeful one. He learns to face the reality that some battles cannot be won, yet he never stops fighting for his patients.

His abilities as a surgeon are nothing short of superhuman. He possesses incredible speed, precision, and stamina, capable of performing solo operations for over twenty-four hours or operating on dozens of patients simultaneously. He has performed surgeries on himself under duress and can reattach limbs, transplant organs with no risk of rejection, and diagnose illnesses with a single glance. His skills extend to veterinary surgery on animals ranging from killer whales to bears, and he has even encountered and treated supernatural beings. Beyond medicine, he is a resourceful and ruthless combatant, using his surgical tools like scalpels as thrown weapons and defending himself with surgical tubing or his bare hands when necessary.