Jean-Paul Sartre

 was a human philosopher that once said, "We are all alone in the universe." Susan Foreman wrote about this in her 27 March diary entry, and wondered if Sartre was a renegade Time Lord like herself. (PROSE: Time and Relative)

Ruby Duvall only knew of Sartre's existence from a joke written on the bathroom wall at the BBC:
 * To be is to do – Descartes.
 * To do is to be – Sartre.
 * Do be do be do – Frank Sinatra.

(PROSE: Iceberg)