The most famous irrational number in mathematics - the ratio of the circumference of a circle to its diameter - is Pi. Pi's existence has been known since 1650 BC. Its value estimated at that time to be about 3.14. Today, with the use of computers, we know it to greater than 10 billion decimal places.

Since Pi is both irrational and transcendental, it is impossible to find a square whose area is equal to that of a circle.

This has led to the labeling of people who attempt to do seemingly impossible acts as "circle-squarers."

Pi = 3.141592653589...