Donald Bruce was Security Chief of the World Zone Authority, appointed to the position by Ramón Salamander. In 2018, he was sent for by Giles Kent to test the Second Doctor's impersonation of Salamander. Though perhaps slightly rough in his methods sometimes, he was essentially a fair man, ensuring that arrested Controller of the Central European Zone Alexander Denes was comfortable.
After questioning Jamie McCrimmon about finding "Salamander" and Kent together, he realised that someone was impersonating Salamander. He started to doubt Salamander's methods of dealing with his enemies when Denes and Fariah Neguib were killed. He eventually turned against Salamander after discovering that Salamander was trying to take over the world, and helped the Doctor defeat him. (TV: The Enemy of the World)