David Cooke, also known as Dave, was a cleaner at Torchwood One. After years of working for Torchwood, he was caught up in a containment breach and encountered a shapeshifter who took his form and memories in front of him. The shock of this caused Dave to have a fatal heart attack and the alien imposter hid his body in Locker 15 in the basement of Torchwood Tower.
Due to the routine administering of Retcon to support staff, the alien's memories became confused and it actually believed itself to be Dave. The imposter retired shortly after Ianto Jones was hired in March, 2005. In 2007, the truth was finally discovered when the alien Dave was brought back to Torchwood after the security device it had left sealing off Locker 15 had begun to erase minds, with Dave's body being found in the process. (AUDIO: Locker 15)