We use pi all of the time, but where does pi really come from? Pi has been used for thousands of year, and it's number is 3.14159. It is attributed to Ahmes, the Egyptian scholar.
http://answers.ask.com/Science/Mathematics/who_inv...

It was discovered by the fact that the circumference of any circle when divided by its diameter is equal to pi. The earliest evidenced conscious use of an accurate approximation for
http://wiki.answers.com/Q/How_was_pi_invented

Pi was chosen as the letter to represent the number 3.141592. because the pi in Greek,
http://www.chacha.com/question/howwaspiinmath...

Pi has been known for so long that it is quite untraceable. The first theoretical calculation seems to have been carried out by Archimedes of Syracuse.
http://www.kgbanswers.com/whoinventedpi/4884083
