Pyrrho

Pyrrho (360-270 BC) was a Greek philosopher and the founder of skepticism. While visiting the planet Marinus, the Doctor advised Tarron, an inhabitant of Marinus, to read Pyrrho's works, and 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.