Harry Mailer

Harry Mailer was an inmate of Stangmoor Prison who was scheduled to be subjected to the Keller Machine. He staged an unsuccessful escape attempt, then shortly afterwards took control of the prison with the aid of the Master, who used him to hijack the Thunderbolt missile. Mailer was shot and killed by the Brigadier just as he was about to kill the Third Doctor. (DW: The Mind of Evil)