Federator was the title of the ruler of a three-planet Federation. The First Federator overthrew the Sumaran Empire on Manussa by defeating the Mara, sending it to the Dark Places of the Inside.
Five hundred years later, the Mara attempted to re-manifest with the help of Tegan and Lon, the son of the Federator at that time. It was stopped by the Fifth Doctor. (TV: Snakedance)