City Administrator was a title in use by the Sensorites. Sensorite City Administrators could be identified by a black collar on the grey bodysuits worn by all Sensorites. It was the City Administrator's duty to protect the one who ruled.
When the First Doctor and his companions visited the Sense Sphere, the City Adminstrator mistrusted the humans and plotted to kill them. He also took advantage of the situation to rise in power: he kidnapped the Second Elder and impersonated him, and when the Elder was killed, the City Administrator became Second Elder. When his crimes were found out, he was banished to the outer wastes, never to return. (TV: The Sensorites)