The Operator

The Operator is an Time Lord from Gallifrey, and one of the most intelligent beings in the entire universe, surpassing even of the greatest geniuses of the galaxy.

Shen the Operator escaped Gallifrey just before the Time War began, he had started to create a planetary scale mega-structure called the Citadel. With the use of his Operator's TARDIS. He had used it to power the Citadel, and capable of time travel.

On his third incarnation, the Operator was confronted by an entity who said was the God of Time but was dying. He had selected the Third Operator to be his successor due to his understanding of the most difficult of concepts (time, space, etc), and also his name. The God of Time felt the Operator is a fitting name for someone who would be able to alter Time, and "operate" it from within his Citadel.

Since he departure of Gallifrey, the Operator has only regenerated 3 times.