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 duringNinth Doctorst- 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 torn apart by carniverous Sollogs, after he jumped into a swamp when the Doctor chucked the Mymon key in.
He seems to be a time traveller, as he mentioned seeing a Nanobomb destroying a mountain range when only one Nanobomb existed at the time of Night of the Humans.
Notes
Precisely what body the Doctor was in when he last caught Slipstream was never specified. The Eleventh Doctor reflected that it had been 'years and regenerations' since he'd last seen Slipstream, but given Slipstream's knowledge of the Time War, the Ninth Doctor seems the most likely candidate
