Archimedes

Archimedes (287-212 BC) was a Greek mathematician and scientist, generally regarded as one of the greatest thinkers in history.

The First Doctor (PROSE: City at World's End) and the Eighth Doctor (PROSE: Fallen Gods) claimed to have met Archimedes. The Third Doctor and Archimedes took a walk on a beach near Athens. (PROSE: Island of Death)

The Sixth Doctor read his name in a collection of business cards of geniuses to consult for a problem of time slip. He defined him "fascinating chap, but a bit wet". (TV: The Two Doctors)

The Ninth Doctor recalled to Jackie Tyler that he once made lemonade with Archimedes. (AUDIO: Retail Therapy)

Other references
During his show, Herbert Clegg made a joke about him and his notorious claim "Eureka!". (TV: Planet of the Spiders)