Jack Hammer, also known as Jack Hanma, is a prominent character in the anime and manga series 'Baki the Grappler.' He is the half-brother of the main protagonist, Baki Hanma, and is known for his immense physical strength and determination. Jack's character is driven by a desire to surpass his father, Yujiro Hanma, and become the strongest fighter in the world. Despite his brutal and sometimes reckless approach to fighting, Jack is a complex character who struggles with his identity and the consequences of his extreme training methods.