The character formally named Chief Lion (ボス, Bosu), known as "Boss," leads the Shishigumi, a lion gang operating in the Black Market.

Chief Lion is a large lion bearing prominent scars over both eyes, resembling a mask. He wears glasses, a suit and tie, uses a cane, and is frequently depicted smoking large cigars. His personality exhibits cruelty and a lack of compassion. He ritualistically forces herbivore prey to strip before consumption, believing the shame and fear enhance the meat's flavor through increased blood flow. He exclusively targets white-furred herbivores, motivating the Shishigumi's kidnapping of Haru.

As the main antagonist of the Meteor Festival arc, Chief Lion orders Haru's abduction for his consumption. When Legoshi intervenes to rescue Haru, Chief Lion attempts to shoot him but is stopped and killed by Louis. This makes him the first significant character killed following Tem's murder at the series' outset. His death enables Louis to assume leadership of the Shishigumi.

Chief Lion's narrative function centers on establishing the Shishigumi's threat and catalyzing Louis's pivotal character development. His narrative presence is confined to the core Meteor Festival events.