Leslie Johnston

 was one of the "holy trinity" of cadets at Sandhurst Military School during the mid-20th century, along with Alistair Lethbridge-Stewart and Walter Douglas. (PROSE: The Forgotten Son)

After Sandhurst, Johnston chose a different path to both Lethbridge-Stewart and Douglas and soon left the British Army. He resurfaced in May 1969 working for the Vault, in a secret citadel beneath London. He was one of the very few who knew the real identity of the mysterious General who ran the Vault. His experiments with Yeti left over from the London Event was stopped by Lethbridge-Stewart and Air Vice-Marshal Ian Gilmore. Despite this, the General pulled some strings which saw to Johnston being set free once again. (PROSE: The Dogs of War)