Jirou, renowned as Knocking Master Jiro, emerged as a legendary Gourmet Hunter. His origins trace to an upbringing by Guinness, one of the Eight Kings, who fed him Nitros in infancy. This infused his body with dense, powerful cells, granting strength rivaling an Eight King or pure Appetite Demon and earning him the title "Rampaging Beast" before his tutelage under Acacia.

He ascended as one of three disciples to the Gourmet God Acacia, alongside adoptive brothers Ichiryu and Midora. Youth revealed a prideful, aggressive, and comedic spirit; he teased Midora relentlessly and challenged Ichiryu in competitive sibling clashes. Acacia’s discipline instilled a lasting fear of heights. Centuries softened his demeanor into a jovial, sake-loving persona, though rare sorrow surfaced when he witnessed environmental ruin—like a barren desert once rich with cherished ingredients.

Visually, Jirou manifested as a frail elder with a pompadour and goatee, draped in ragged attire. He could reshape his form via "Knocking": muscle stimulation swelled him to youthful vigor, while seal releases unlocked the "Rampaging Beast"—a taller, darker-skinned figure with wild hair and elongated limbs. Full unsealing restored his muscular prime, skin darkened and irises ablaze.

His signature "Knocking" martial art targeted pressure points to paralyze, immobilize, or induce harmless sleep. Techniques spanned "Medium" (celiac plexus strikes) to "Well Done" (full-body paralysis). His apex technique, "Grand Knocking," slowed Earth’s rotation, unleashing global disasters. He wielded the Wolf King’s fang as a knuckle duster, unleashing spiraling energy strikes like the "Rising Wolf Guinness Punch."

A lifelong partnership bonded him to chef Setsuno; together they hunted rare Gourmet World ingredients. Their intimacy echoed in affectionate nicknames ("Secchan," "Jiro-chan") and Setsuno styling Toriko’s hair after Jirou’s pompadour. As grandfather to Teppei, he trained him in Gourmet Hunter arts, inspiring Teppei’s Saiseiya vocation to preserve habitats. Even retired, Jirou hunted for pleasure, pursuing the ultimate ingredient GOD.

His Full Course Menu comprised:
- Hors-D'oeuvre: Hundred Leaf Clover
- Soup: Magma Consomme
- Fish Dish: Royal Land Shark
- Meat Dish: Ashurasaurus
- Main: E.T. Rice
- Salad: Grana Lettuce
- Dessert: Oasis Melon
- Drink: Doham Spring Sake

After centuries of exploits, Jirou perished. Posthumous revelation identified him as a reincarnation of a Gourmet God’s second son.