Zio was a 24th century Akritirian. In the year 2367, he was found to have committed crimes against the authoritarian Akritirian government. As that government had a policy of irreversible convictions, all imprisonments are permanent. By 2373, Zio had been a prisoner in the Akritirian maximum security detention facility for over six years. During his time of incarceration, he had composed a lengthy manifesto.
In that year, Tom Paris and Harry Kim were imprisoned in the facility. Tom was stabbed, and in desperation Harry made a deal with Zio—Harry would take him with them upon escape with if Zio gave him medical supplies to care for Paris' wound. Zio and Harry went through with a plan to disable the force field that sealed the access chute, but they found that the prison was in a huge space station, as the hatch only led to open space.
Zio had learned to overcome the mentally debilitating effects of the clamp, a control device that was attached to each prisoner, which Kim attributed to Zio's probable insanity. Zio's attitude was in fact vicious, in that he wanted Harry to kill Tom to avoid a burden on the inmates' supplies. (VOY episode: "The Chute")
- Zio was played by actor Don McManus.