After Jo Grant arrived in his time, the Controller welcomed her and made her comfortable in order to gain her trust. He convinced her he was working hard to ensure the safety of the Third Doctor, and when he captured him, brought them together. The Doctor accused him of being a quisling, but he protested there was nothing anyone could do against the Daleks.
The Doctor and Jo escaped but were found some time later. The Controller, convinced the Doctor could overthrow the Daleks, allowed them to pass freely. However, a guard overheard the conversation and reported his betrayal to the Daleks. Just before they exterminated him, he declared, "Who knows? I may have helped to exterminate you." (TV: Day of the Daleks)