The "Father of Geometry"
Who was he?
We know that he taught at Alexandria, the capital city of ancient Egypt and home to a legendary library. It is believed that he taught there sometime between 320 B.C. and 260 B.C.
The rest of his life must be left up to guesswork. Most people believe he was born around 300 B.C which would make him older than Archimedes, another Greek Mathematician, who was born in 290 B.C. Some historians don't support this belief, though. So no one is even sure of that.
Euclid's Windmill Proof
This is the proof Euclid included in the Elements for the Pythagorean Theorem.
This is one of the oldest pieces of the the Elements. a scrap of papyrus from around A. D. 100. The diagram in the lower corner is from Book II, Proposition 5.
What did he do?
Why do I have to know about him?
Non-Euclidian geometry is based on a sphere and is much more complex but much less practical.