The Daleks regularly forced the Controller to increase production on the mineral mining for the continual expansion of their empire. The Controller protested that the extra work would kill the slaves but he was ignored.
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 argued there was nothing anyone could do against the Daleks and that his work was saving lives from an even worse fate.
The Controller gave the Doctor and Jo a short but insightful story of the wars which devastated Earth, allowing the Daleks to invade because there was no power strong enough to fight them off. He was also dismissive of the resistance, though this was probably because he didn't think there were enough of them to pose a serious threat, and they regularly concentrated their attacks on small targets instead of something vital.
The Doctor and Jo escaped but were found some time later. The Controller, convinced the Doctor could overthrow the Daleks and save the future, 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." Indeed, the Controller allowing the Doctor and Jo to escape enabled the two to return to their own time and alter the future, saving the Earth from the Dalek invasion. (TV: Day of the Daleks)