Who Invented Pi?

Who invented pi? Tricky question!   Mother Nature invented it!   Well, that may not be the answer you were expecting, Ada the Philologian understands.   So, let's approach that question from a different angle:

Q1. Who first discovered the principle of pi?

A1. Most definitely a long long time ago, quite possibly pre-dating written language.   Ada the Philologian is enamoured with the idea of mathematically-inclined Mesopotamians.   So, let's say the discovery was likely of the same era as the first wheel - over 5500 years ago.

Q2. Who started using the Greek letter pi to express the mathematical ratio of a circle's circumference to its diameter?

A2. It is a Greek letter, so we want to assume the symbol originated with the Greek people.   But sorry, Ada the Philologian cannot confirm this.   The first scientist to use pi to express the ratio was a Welsh mathematician named William Jones in 1707.   Ada's exhaustive research suggests that the symbol pi was not widely adopted until the 19th century.   It is rather surprising, isn't it?

As you can see, there is no simple answer to "who invented pi?".