Which of the following Greek thinkers discovered the value of pi?

None. The existence of Pi was estimated by the ancient Egyptians, ancient Indians, and Babylonians many hundreds of years, B. C. The Greek philosopher, Archimedes, was later able to calculate the value of Pi using geometry to a great degree. It wasn't until 400 - 500 A. D. that Chinese mathemetician Zu Chongzhi found that 553/113 was a very accurate approximation of the value of Pi, so much so that his value held for the next 900 years.