Leonhard euler (1April 5, 707 ~1September 8 1783) was a Swiss mathematician and physicist. He is called one of the two greatest mathematicians in history by some mathematical historians (the other is C.F.Gauss). Euler was the first person to use the word "function" to describe expressions with various parameters, such as y = F(x). He was one of the pioneers who applied calculus to physics.

The definition of function is given by Leibniz in 1694.