Black Jack is a medical mercenary, selling his skills to the highest bidder. He is a shadowy figure, with a black cloak, eerie black-and-white hair, a scar across his face and partially black skin. Black Jack cures patients indiscriminately, from common folk to presidents and yakuza leaders. To his VIP patients, he charges absurd sums. All this has given him a reputation for callousness and greed which he gleefully cultivates. However, to the reader it is clear that Black Jack actually is a good man: he is anti-wealth and anti-prestige, and believes he is actually doing rich people a favor by removing their material wealth. The opposition to wealth and power is a common theme in Tezuka's work: powerful men are almost always portrayed in a negative light.

Throughout his life, Black Jack learned some harsh lessons and has to face the reality that there are times he cannot go against the forces of nature. In difficult and tricky situations, he is a quick thinker and is able to fool others easily. Besides being an expert in surgeries, he is also a skilled combat fighter who makes use of his surgical tools that he hides underneath his cape. Although, he is perfectly capable of fighting with his bare hands, even delivering a single knock-out punch to the stomach at one point. He also shows that he is highly responsible for his patient's safety and well-being, which explains his high pricing. He even goes to the lengths of deceiving his patients to make sure they heal properly.

He also cares for and is deeply appreciative of people who change his life, such as Dr. Honma, who saved him through surgery once. Black Jack is also very prideful and hates being made fun of, or things he deems important desecrated.