Keeper of Traken
The Keeper of Traken, or simply The Keeper, was a Keeper of the planet Traken and of the Traken Union. They had the power to control everything in the Union, making sure everything was harmonious.
The Keepers ruled for thousands of years with the power of the Source. This power was great, allowing Keepers to take control of minds and to materialise anywhere. Drawing on all the minds of the Union, they protected the planets. Every thousand years, a new Keeper would be chosen as the old one died.
As his final time approached, the Keeper contacted the Doctor for his help. He explained about the Melkur that existed on Traken and asked him to help prevent the evil from taking control of the bioelectronic Source that was the keystone of the Keeper's power and of Traken civilisation. The Doctor and Adric agreed and the Keeper pulled the TARDIS to Traken.
The Keeper had chosen Tremas as his successor, but when Tremas came under suspicion with the Doctor and Adric about the Melkur, Kassia was chosen by the consuls to replace the Keeper. However, she was working with the Melkur.
When the Keeper died, she took his place and became connected to the Source. As soon as she was, she was taken over by the Melkur who then became the new Keeper. Adric and the Doctor were able to sabotage the connection to the Source and force Melkur out of the Keeper's sanctum, allowing Luvic to take Melkur's place and become the new Keeper of Traken. (DW: The Keeper of Traken)
When a wave of entropy swept across part of the universe in 1981, Traken was destroyed, the Keeper dying with the planet and the rest of the Union. (DW: Logopolis)