HAPPY PI DAY!
Nobody knows how pi was discovered. What we do know that pi has been known for over thousands years.
It is possible that it was the Babylonians in 2000 BC who used 3 1/4 as an approximation to pi, or the Egyptians, who used 256/81... History teaches us that the first mathematician to calculate pi with reasonable accuracy was Archimedes, around 250 BC; then when Newton and Leibnitz developed calculus in the late seventeenth century, more formulas were discovered that could be used to compute pi.
The connection between all of them? Beards, beards, beards, and beards. (Editor's note: Newton and Leibnitz wished they had beards, and wore their wigs on their heads and not chins)
Babylonians: Nebuchadnezzar
Ancient Egyptians
Archimedes