Who was the first person to say the extension of the spring is proporsional?

The first person to articulate that the extension of a spring is proportional to the force applied to it was Robert Hooke in the 17th century. This principle is now known as Hooke's Law, which states that the force needed to extend or compress a spring by some distance is proportional to that distance, within the elastic limit of the spring. Hooke published this concept in his work "Micrographia" in 1665.