One of the recurring characters of Grappler Baki. Also known as "Jack Hammer" in the early romanization.
Jack Hanma is the first offspring of Hanma Yujiro born to a Canadian mother, Diana Neil, after Yujiro raped Diana during his time as a mercenary after he found out that Diana was sent as a spy by the United States to kill him. Since his youth, Jack swore to kill Yujiro in combat to get revenge for his mother for the trauma Yujiro has caused. To this end, Jack fanatically trains to become stronger while disregarding anything he deems "unnecessary" such as eating or bathing, to the point that his body became bone-tight skinny and that he could only move by his sheer will to live. Noticing his determination, an American scientist offered a "super steroid" that massively increases his muscle mass, which allowed him to endure the rigorous training he partook in.
While generally reserved and quiet outside of the fight, Jack is a ferocious fighter that will use any means necessary to obtain more strength and win, even if it means shortening his lifespan. He regularly takes bottles of steroids and stimuli as a part of his training (which he was able to endure the side effects of due to his "Hanma blood"), and has multiple body modification surgeries to increase his stature. He is best known within the series for inventing "Goudou", a "fighting style of the weak" consisting of biting the opponent on the critical parts of their body to defeat them.
