Atza, along with Ortezo, was a Mogarian passenger on the Hyperion III in 2986. They prevented Bruchner from plunging the ship into the Black Hole of Tartarus, but then hijacked it.
They were really in league with Rudge to steal the ship's vionesium cargo, which they saw as having been stolen by the Earth Empire from Mogar. While on the bridge, Doland killed Atza and Ortezo by throwing a liquid at them which damaged their suits. This exposed them to oxygen, killing them. (TV: Terror of the Vervoids)