Pyrrho

Pyrrho was a Greek philosopher and the founder of scepticism. While visiting the planet Marinus, the First 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")