Kurt (Shakedown: Return of the Sontarans)

Kurt was a very wealthy businessman, possibly with a shady past.

Biography
Kurt was part of Lisa Deranne's Tiger Moth crew. He and Deranne were the only two to survive when Sontarans boarded their solar-yacht searching for a Rutan agent, and he resolved to hire a new crew and re-enter the solar-yacht races. Prior to this event, he claimed to have met a "dentist" who had a perchant for screwdrivers and who told him about Sontarans and their weakness. (HOMEVID: Shakedown: Return of the Sontarans)

Behind the scenes

 * The novelisation of the story, expanded this by having him encounter the seventh Doctor during a Sontaran invasion of a human occupied world (the Doctor was there formenting rebellion against the humans, and then promptly switched his focus to the Sontarans upon their invasion). Kurt was a smuggler who ended up in a cell with "the infamous rebel general Smith".