Cessair of Diplos

Cessair of Diplos, also known on Earth by a variety of aliases, was a long-lived fugitive criminal.

Biography
Cessair was wanted for multiple counts of murder and for the theft of the Great Seal of Diplos (which was actually the third segment of the Key to Time). She escaped Diplos and took three Ogri from Ogros (which contravened Article 7594 of the Galactic Charter).

Her servants and she were eventually captured. They were returned to Diplos with the Megara, sentient justice machines. En route, Cessair escaped, took control of the ship and diverted it to Earth. She hid on the primitive planet, her starship hidden in hyperspace.

Cessair hid on Earth for four thousand years, adopting a number of identities. These included the the Celtic war goddess known as the Cailleach, Lady Morgana Montcalm, the reclusive Mrs. Trefusis and Miss Vivien Fay. Despite the changes in identity, she always controlled the land around the stone circle where the Ogri rested and where, in hyperspace, the starship waited.

In the 1970s, the Fourth Doctor came to Earth to find the third segment of the Key to Time. Romana was kidnapped by Cessair and was brought to the starship in hyperspace. The Doctor followed her, but accidentally released the Megara, who sentenced him to death.

After a gruelling trial, the Doctor made the Megara realise Cessair's true identity. Having established her guilt, they sentenced her to perpetual imprisonment and transformed her into another stone in the circle. (TV: The Stones of Blood)