The Mistress (The Choice)

The Mistress was a time traveller. She had a version of K9 as a companion. (AUDIO: The Choice, The Search)

She claimed to be 487 years old. (AUDIO: The Choice)

Behind the scenes

 * The character, played by Lalla Ward, was heavily implied to be Romana II traveling with K-9 Mark II following the events of Warriors' Gate. Legally, she could not be referred to as such as BBV Productions did not have permission from the BBC to use the actual character.
 * Throughout the two stories in which she appears, the character is only referred to with various formal forms of address. No name is ever given.