Who came up with pi?

William Jones, a mathematics teacher, first came up with pi; however, Leonard Euler is often credited with its introduction into mathematics. Jones wrote in his second book "Synopsis" that he believed pi was actually an irrational number, and the ratio should be represented by a symbol.

Before pi became widely used, the ratio was called "quantitas in quam cum multiflicetur diameter, proveniet circumferencia" a phrase that is Latin for "the quantity which, when the diameter is multiplied by it, yields the circumference." The fractions 355/113 and 22/7 were often used for pi. However, those ratios are not an accurate representation of the true ratio of pi.