Heron was a Greek mathematician who lived around 0 AD and made significant contributions to mathematics. One of his most important contributions was Heron's formula, which allows users to calculate the area of a triangle when the lengths of all three sides are known. The formula calculates area as the square root of s(s-a)(s-b)(s-c), where s is equal to (a+b+c)/2 and a, b, and c are the lengths of the three sides of the triangle. The document provides an example of using Heron's formula to calculate the area of a triangle with side lengths of 3 cm, 5 cm, and 6 cm.