Jiro is a legendary figure within the world of gourmet hunting, widely known by his title, the Knocking Master. Despite often appearing as a frail and hunched elderly man with a distinctive pompadour hairstyle and a goatee, this appearance is deceptive. He possesses the ability to alter his own body structure through a specialized technique, allowing him to transform into a far younger, taller, and more muscular form, often with his hair and goatee turning black. In this state, his true physical power becomes evident. This transformation is not a fixed state; he can modify specific parts of his body, such as enlarging only his upper body and arms, to suit his needs.

His background is deeply entwined with the highest echelons of power in his world. Jiro was one of the three disciples of Acacia, the revered Gourmet God, making him the adopted brother of Ichiryuu and Midora. Before this, however, he was raised in a wild and brutal environment by one of the most powerful creatures in the world, the Wolf King Guinness, one of the Eight Kings. During this early period, he was known by the sinister title of the Rampaging Beast. His immense and uncontrollable strength as a child caused Acacia to fear his might, leading the Gourmet God to seal a portion of his power using knocking techniques in order to teach him control and proper technique. This sealing is directly responsible for his ability to change his appearance and is why he is over five hundred years old, having been alive since the time of his brothers' last great conflict.

In terms of personality, Jiro is generally portrayed as a friendly, easygoing, and mellow individual who is almost always seen smiling. His most defining personal trait is his enormous fondness for alcohol, which he considers to be life itself. He is known to make constant trips to locations like the Drunken Archipelago and believes that booze brings people together across any era. The simple act of sharing a drink with him is enough to earn his eternal gratitude. This is demonstrated when he revives the chef Komatsu from a stopped heart and agrees to rescue the protagonist Toriko from the dangers of the Gourmet World, asking for nothing in return. However, this gentle demeanor masks a ferocious side. When angered or when his seals are released, he becomes a truly terrifying and formidable force, reverting to the brutal nature of his youth. Teppei, his grandson, recalls that a rare moment of Jiro stopping his smiling was when he saw a former hunting ground turned into a barren wasteland, an event that deeply saddened him.

His role in the story is that of a guardian and a symbol of ultimate power. As a retired legendary hunter, he is one of the three strongest individuals in the world. He serves as a mentor figure, having trained his grandson Teppei in the arts of gourmet hunting and knocking. His deep care for Teppei is evident, and his sadness over environmental destruction inspired Teppei to become a Saiseiya, someone who restores nature. His key relationship is with his longtime partner, the chef Setsuno. During their youth, they traveled and hunted together in the Gourmet World, a partnership that runs so deep that their full-course menus share the same source ingredients. Their bond is intimate, and Setsuno's affection for him is shown when she styles the protagonist Toriko's hair into a pompadour.

Jiro's development is tied to the unsealing of his power. The seals placed on him by Acacia suppressed the overwhelming might and wild ferocity of the Rampaging Beast. As he removes these seals in battle, his appearance changes into progressively more bestial and powerful forms. In his final form, he gains darker skin, longer black hair, black sclera, and dramatically increased muscle mass. When his power is fully unleashed, his personality also shifts, and he gains access to his most devastating techniques, including the ability to briefly stop time.

Jiro's notable abilities are almost entirely centered on his mastery of Knocking. This art is typically used to non-lethally paralyze living creatures, but Jiro has elevated it to an inconceivable level. His skill is so profound and delicate that he can obliterate the head of a powerful creature like a Nitro with a simple finger flick while simultaneously paralyzing it. He can use knocking guns to take down hundreds of high-level beasts in rapid succession without a single wasted shot. He can also use his bare hands to perform Hand Knocking with just a thumb or a finger flick. His ultimate technique, Grand Knocking, involves striking the ground with his fist with enough force to nearly stop the rotation of the entire planet for a split second, paralyzing almost all life on Earth. As a testament to his physical strength, he can wield the Rising Wolf Guinness Punch, a spiral blast of energy channeled through a special glove that takes the shape of a wolf's head and is powerful enough to reach outer space. Furthermore, Jiro is a master of Food Honor, a state of heightened concentration and appreciation that cuts down useless movements and conserves calories. Through this, he has achieved Food Immersion, which allows him to absorb and store nearly unlimited nutrients from his meals, granting him immense stamina and the ability to survive for abnormal spans without food or water.