Pythagoras

Pythagoras was an Ancient Greek philosopher and mathematician. (PROSE: Empire of Death)

Biography
The Doctor met him before their fourth incarnation. (AUDIO: The Labyrinth of Buda Castle)

The Fourth Doctor recalled Pythagoras as a lovely fellow who was good at billiards. (COMIC: Gaze of the Medusa)

The Thirteenth Doctor claimed to have borrowed some sunglasses from either Pythagoras or Audrey Hepburn. According to the Doctor, he wore shades when he was drunk. (TV: The Ghost Monument)

Philosophical beliefs
Pythagoras believed in metempsychosis, i.e., transmigration of the soul, also known as reincarnation. (PROSE: Empire of Death)

Scientific achievements
Pythagoras proved that the Earth revolved around the the sun 19 centuries before Copernicus. (COMIC: Gaze of the Medusa)

By plucking a string, he discovered that the relation of a note to its overtones is always a fraction. (PROSE: The Algebra of Ice)

Pythagoras proved a theorem that determined properties of a hypotenuse. (PROSE: Byzantium!)