According to History Today, William Jones created pi in 1706. This mathematics teacher used the symbol to refer to the constant ratio of any circle's circumference to its diameter.
History Today clarifies the common misconception that the Swiss mathematician Leonhard Euler is the one who introduced the symbol by stating that the symbol ? appeared in William Jones' book entitled "Synopsis Palmariorum Matheseos, or A New Introduction to the Mathematics" a year before the birth of Euler. According to History Today, although William Jones was not able to prove it, he was the first to assert that pi is an irrational number, or a non-repeating infinite sequence of numbers, that can never be fully expressed in numerical form.