The value of pi (π), the mathematical constant representing the ratio of a circle's circumference to its diameter, has been known since ancient times, though it was not "invented" by a single individual. Instead, the understanding of pi evolved over centuries:

1. Ancient Egyptians and Babylonians (around 1900–1600 BCE): Both civilizations had early approximations of pi. The Babylonians used 3.125 (or $\frac{25}{8}$), while the Egyptians estimated pi to be about 3.16, as found in the Rhind Mathematical Papyrus.

2. Archimedes of Syracuse (287–212 BCE): The Greek mathematician Archimedes is often credited with the first rigorous approach to approximating pi. He used polygons inscribed and circumscribed around a circle to show that $\pi$ was between $\frac{223}{71}$ (about 3.1408) and $\frac{22}{7}$ (about 3.1429).

3. Liu Hui (circa 3rd century CE): A Chinese mathematician, Liu Hui, refined Archimedes' method and computed pi to about 3.14159.

4. Modern Developments: In the 17th century, mathematicians such as Ludolph van Ceulen calculated pi to 35 decimal places, and later, it became possible to compute pi to millions of digits using computers.

While no single person "invented" pi, it was Archimedes who laid the foundation for calculating pi with greater precision, and subsequent mathematicians refined this value further.

Would you like more details or have any questions?

Here are 5 related questions:

1. How did Archimedes calculate the value of pi?
2. What methods are used today to compute pi to billions of digits?
3. Why is pi an irrational number?
4. How has pi been used in real-world engineering and science?
5. What are the other famous approximations of pi used in ancient cultures?

Tip: Pi is a transcendental number, meaning it is not the root of any non-zero polynomial equation with rational coefficients!