Kid Chaos was the boxer personae who appeared on behalf of the Chaos entities residing in chaotic space who were trying to contact Chakotay in 2375.
Kid Chaos appeared to Chakotay during a series of vision quests after the aliens affected his DNA to reawaken a genetic marker for sensory tremens, a cognitive disorder whose symptoms include auditory and visual hallucinations. Via those hallucinations, Chakotay was able to perceive the aliens, who existed on a perceptual wavelength undetectable to most humanoid senses, enabling them to instruct him on how to escape chaotic space. (VOY: "The Fight")
Kid Chaos was played by regular background actor Tarik Ergin who received no credit for this appearance.