Caliban had participated in the Mutai until a final fight with Gyor ended his fighting days.
In 2258, Walker Smith arrived at Babylon 5 to participate in the exclusively non-human Mutai fight circuit. He hoped that the publicity would help him reignite his boxing career. Initially denied from participating, Smith received aid from Caliban, and eventually entered the competition. Caliban helped him train and understand the nature of the Mutai -- apparently out of respect for Smith's courage and for a desire to settle the score with Gyor, whom Walker had to fight to get accepted. With Smith's entrance into the competition, he paved the way for other humans to join.