Which mathematician invented the formula for perimeter?

Although some have said Archimedes, my opinion is that the formulas for area and perimeter of a rectangle were well known before his time (300BC). The Babylonians in 1500BC knew how to create Pythagorean triples, so I wouldn't be surprised if they knew this.

Archimedes did discover more difficult formulas, such as perimeter and area of a circle, and volume of a sphere and a cone.