The Curator was an elderly form of the Doctor who had retired from his adventurous ways to become the "humble curator" of the Under Gallery. There was only one Curator. However, his form varied. (AUDIO: Crossed Lines) He chose to take on the appearance of former incarnations they had been, including the Fourth (TV: The Day of the Doctor), the Sixth, (AUDIO: Crossed Lines) and the Eleventh Doctors. (AUDIO: The Keys of Baker Street) He suggested to the Eleventh Doctor that his choice was to revisit "just the old favourites". (TV: The Day of the Doctor)