He was a former patient of Molly O'Sullivan. When she left with the Eighth Doctor in 1918, she gave David Walker the keys to 107 Baker Street. (AUDIO: The White Room)

David lived in the house until the 1970s. In the interim, he married a woman named Isabelle and they raised their two sons, one of whom was named Nigel, in the house. He stopped driving in 1962. He was blind but the Reborn Master returned his sight. (AUDIO: Eyes of the Master)