His ringname is Jack Hammer (ジャック・ハンマー, Jakku Hanmā).
Jack's driving force is wanting to defeat his father, Yujiro Hanma, to avenge his mother who was raped by him. Jack turned into a monster without balance who only cares about becoming stronger to take revenge. It can be said that he is sometimes too confident in his strength. Trains too much for his body to handle, forcing him to resort to stereoids and other medical methods in order to keep his strength growing steadily. Is too obsessed with beating Yujiro and avenging his mother, to the point where he is blinded by that dream. He doesn't know a lot of techniques and often fights head-on.
He sees his brother, Baki Hanma, as a rival, but also likes and cares for him deep in his heart as they have the same goal in surpassing Yujiro. Jack also seems to have some feelings for his younger brother's girlfriend, Kozue. When he first meet her in the Maximum Tournament, he flirted with her. But maybe he did it only to provoke his brother.
Jack's intelligence is relatively average. Although he has shown himself to be a slightly bit of a combat genuis from times to times (as he was able to counter Shibukawa's Aiki), that is likely due to his lineage as a Hanma and the son of Yujiro Hanma.
Jack trained so hard that his muscles became completely destroyed. He took a lots of steroids to strengthen his body, and his muscles became extremely big and strong. Unfortunately, an amount of drugs eventually managed to destroy his body again, and drastically reducing his life expectancy in the process. But later, Jack managed to repair his body and he became even stronger. In the second series of the manga, he underwent surgery to made him taller and stronger. Kureha Shinogi carried out the operation, and thanks to that fact the desired effect was achieved. Kanji Igari stated that Jack is even bigger than Mount Toba.
His physical features include blue eyes, a piercing gaze and short blonde hair and rather large eyebrows. He's often wearing a blue t-shirt, long jeans or shorts. In the third season of the anime, Jack's eyes are brown.
Jack is an extremely tall and muscular man. His initial height was 6'4, which changed to 7'0 after the Maximum Tournament thanks to Shinogi Kureha's limb-lengthening surgery, and finally to 8'0 after Jack's fight with Pickle, which was once again achieved by the limb-lengthening surgery.
Baki the GrapplerEdit
Like his brother Baki, he has since childhood wished to surpass his father Yujiro Hanma in strength and martial ability. His obsession to defeat his father led to extreme over-training at various fighting gyms which led to the deterioration of his body. He wasn't much more than skin and bones because his body had been damaged by overwork. For example, Jack would punch sandbags for over 12 hours without eating, resting, or even using the restroom. He claimed he will never be able to defeat his father with normal training. After his encounter with the Yujiro-inspired scientist named Dr. John who witnessed Yujiro killing a polar bear, the scientist promises him great results if he tries using a special drug. He received from him a concentrated formula of steroids to match his over-training and gained immense power in the process, though in the process Jack had become even more mentally unstable.
Maximum Tournament SagaEdit
Most Evil Death Row Convicts SagaEdit
After the Maximum Tournament, Jack has Kureha Shinogi perform surgery to lengthen his bones where multiple of his bones were broken and he had his limbs lengthened in 8 places. Jack is then first seen by Kaioh Retsu in a restaurant where Jack orders an entire roasted pig for himself and eats it in 10 seconds, even though Retsu is at first unaware that it's Jack and judges his height, saying it could be more than 210cm. Jack then stands up and walks up to Retsu and says that he just remembered who Retsu was and that he saw him in the underground arena and at the Maximum Tournament. This shocks Retsu and makes him realise that it's Jack. He afterwards wonders on how Jack managed to gain 20cm (Jack was 6'4 the last time they met, meaning that Jack is 7'0 at this point in the series). Jack silently walks away with Retsu looking at him, still wondering on how Jack grew so much in less than a year.
After this, Jack goes on to another restaurant with Kureha Shinogi, where Jack orders a T-Steak and ends up eating the bones like biscuits, leaving the waiters surprised and wondering if he's a professional wrestler. Meanwhile, Kureha compliments Jack's growth rate, calling it a miracle, and explains the limb-lengthening surgery Jack underwent in 8 places after the Maximum Tournament. After he finishes, Jack says that he doesn't care about brotherhood, but he can be the one who gets revenge for Kureha. This is probably a reference to the loss Kureha suffered from Jack's half-brother Baki in the underground arena. It can be also a reference to the fact that Hector Doyle almost killed Kureha's brother Kosho Shinogi.
Later, Jack is seen confronting Sikorsky, the Russian serial killer and one of the five death row convicts. He tells Sikorsky that he is simply an enemy to him and asks where should they fight, mentioning that the police in Tokyo can be annoying. They decide to fight in an empty public bathroom. Jack strikes first with a punch which Sikorsky barely avoids. Sikorsky then grabs onto an emergency fire extinguisher on the ceiling with his thumb and index finger and kicks Jack in the face. Jack shakes off the attack and compliments Sikorsky's finger strength, before questioning for how long he can hold on like that. He charges at Sikorsky again and grabs his leg, making Sikorsky repeatedly kick Jack in the face with the other in order to release himself, but Jack punches Sikorsky so hard that Sikorsky breaks the emergency fire extinguisher and flies of to the end of the bathroom and throws up. After this, Jack and Sikorsky go to a phone booth where an unsuspecting civilian Sho is making a call. Sikorsky enters first and Jack second. After a short fight, Jack knocks out Sikorsky and orders for the phone booth to be transported into the colliseum via a truck. After this, Jack enters the arena while the truck releases Sikorsky and Mitsunari Tokugawa explains the situation to him. Sikorsky then starts yelling loudly before taking off his shirt and screaming: "давай!", which in this context means "bring it on!" in Russian. Sikorsky strikes first and Jack tanks his strikes, only to lift Sikorsky up after Sikorsky tries to push Jack into the wall. Jack throws him into a wall on the opposite side and then rushes to him and kicks him so hard that Sikorsky flies into the audience. Sikorsky then decides to take an old man's staff, as well as a nail from a wall broken by his body while he was being tossed by Jack, and use them as weapons. Jack notices this and lets Sikorsky use the staff as a spear. Sikorsky tries to stab Jack, only for the spear to stop without piercing even his abs. Jack says that unless it's an actual spear it won't pierce his abs. Sikorsky then throws the wrinkled nail in Jack's face, but Jack catches it with his teeth and proceeds to chew it. After a short while he spits the nail out, showing that he almost made it into a gum thanks to his incredibly strong teeth. Seeing this, Sikorsky thinks to himself that Jack isn't human while Jack says that it's time for a switch and that Sikorsky will get a opponent worthy of him. At this point Gaia starts walking into the arena while Jack starts leaving. They meet half-way and Jack gives Gaia a high-five before exiting the arena.
One of his main techniques is the biting, and he can bite hard enough to easily crush wood with his teeth. He claims that his teeth can tear a coconut. Jack could eat a whole roasted pig in 10 seconds and could chew on the bones of a T-bone steak like it was a biscuit, thanks to the amazing power of his teeth. Although he lost all of his teeth, his bite can still damage Izou Motobe when he wears chain mail made of Aramid fibres, which is made for planes and tires. His body is strong enough to surpass drugs, even though he used abnormal amounts of them.
His strength is shown many time in the story: killed a polar bear with his bare fists in the same way his father did, defeating the convict Sikorsky with a punch so strong he lifted the telephone box where they were located in that moment, and withstood his knuckle slash in the underground arena, taking many blows from Mohammad Alai Jr and defeating him, cutting Ali's tongue in the process, fighting with Pickle and making him run away in fear of the only creature that scares him, a wasp.
Despite using brute force to fight, Jack is a very tactical fighter, and is smart enough to counter and outmaneuver his opponents. For example, he made Chiharu Shiba pass out with a special type of a hold where Jack presses two fingers on the gang leader's vital points that are located in the throat (Baki defeated Gaia with a similar way; except that Baki did it with two hands, while Jack only used one hand) and also when he found the weakness of Aiki after being thrown many times and used a similar move to defeat Goki Shibukawa.
- He is based on the legendary British professional wrestler Dynamite Kid.