Zachary "Zack" Cross Flane was second-in-command of the Walker Expedition during the 42nd century.
Profile
Zachary took charge after Captain Walker was killed when their ship crashed on the planet Krop Tor after encountering K37 Gem 5, the black hole that the planet was orbiting. Although he was reluctant and unsure of himself, he nevertheless successfully dealt with the attack by the Beast and evacuated the survivors in a spaceship. He bestowed posthumous honors on his fallen crew, including the possessed Toby Zed and the Ood servants the humans had been forced to destroy. Presumably, after the Doctor and Rose saved him, he then returned to Earth. (DW: The Impossible Planet, The Satan Pit)
- His mention of the Torchwood Archives suggests very strongly that he worked for a future version of the Torchwood Institute, though we do not know if his the other crew members of Sanctuary Base 6 also worked for Torchwood. Alternatively it's possible that Torchwood's existence had simply become common knowledge by the 42nd century much as evidence suggests it had by the 201st century; the Torchwood spin-off, featuring the institute, shows it becoming more and more public as time goes on.