Dev Ashton was an engineer on-board the S.S. Pentallian.
The sentient star Torajii, having already possessed another crewmember, took over Ashton's body to make him kill. Due to the intervention of the Tenth Doctor, Torajii relinquished its hold over Ashton. Erina Lessak worked under him. After Ashton had been possessed, Kath McDonnell tricked the possessed Ashton into being trapped in the stasis chamber, which killed it. (TV: 42)