It’s Ancient History
Pi is so old it was discovered before we had weekdays. The ancient Babylonians and Egyptians came up with formulas that gave a value for pi, but Archimedes of Syracuse gets most of the kudos for proving pi was somewhere between 3 1/7 and 3 10/71. He found it with some help from the Pythagorean Theorum (remember a2 + b2 = c2 ?) and a 96-sided polygon.
This new and exciting number was referred to as “the quantity which when the diameter is multiplied by it, yields the circumference” until nearly two-thousand years later when Welsh mathematician William Jones was the first person on record to connect the value to the Greek letter π. Swiss mathematician Leonhard Euler made it mainstream several years later through contact with other mathematicians throughout Europe.