Pyrrho

Pyrrho (360-270 BC) was a Greek philosopher and the founder of skepticism. While visiting the planet Marinus, the Doctor advised Tarron, a policeman in Millennius, to read Pyrrho's works, as they would be helpful to someone in his line of work. When asked if he had read Pyrrho, the Doctor claimed to have met the philosopher in person. (DW: The Keys of Marinus)


 * It is possible that the Doctor met Pyrrho in the same adventure that he met Alexander the Great, as the two were contemporaries.