Well sorry to have to break it to you Bear but mate it wasn't invented it is a basic mathematical calculation that is infinite - almost like a law of physics you might say. It is a most important mathematical figure use in so many applications least not I wouldn't wonder used for calculating inter planetary shots.
But I do stand to be corrected.
Dinesh I think had it first up with Euclid I have 3.1415 embedded in my mind as reference for when I used to work out the rolling distances of road wheels
Gary's illustration shows this perfectly and is the perfect way to know how it actually works - those crafty Hoosiers!!.
I saw some maths bloke on TV the other day quote it to 1000 decimal places and he was a visiting American mathematician who was matched by an Aussie fellow too - just amazing