Algy was a British Army officer who was with Captain Jack Harkness when the latter spotted Rose Tyler hanging on the mooring rope of a loose barrage balloon while a German air raid was under way in London Blitz on 20 January 1941. He had a relationship with Captain Jack. (TV: The Empty Child)
Later on duty at the Limehouse Green railway yard where the crashed Chula ambulance was stored, he became infected by the gas-mask illness when the virus began to accelerate and become airborne. Transforming into a Gas-Mask Zombie before the horrified Jack's very eyes. He was eventually cured by the Chula nanogenes when the Doctor "emailed the upgrade" once the nanogenes realised what a human was supposed to look like. (TV: The Doctor Dances)