Dirk Slipstream

Dirk Slipstream was a criminal who served time in Volag-Noc after being caught by the Doctor in an earlier incarnation. He was sentenced to fifty years per person he killed during a jewel heist- that's 600 dead working out to about 32000 years. In Night of the Humans, he went searching for the Mymon Key- an object of unlimited power- on the Gyre. Slipstream was presumably killed by carnivorous Sollogs while making one last desperate bid for the Mymon Key.