Galileo Galilei
A legend says that he climbed the Leaning Tower of Pisa, and dropped cannonballs of different weights, to see which would strike the ground first. Even though their weights were not the same, they hit the ground at the same time. Galileo found that objects fall to the ground at the same rate, unless things like wind resistance change the rate. This went against the views of Aristotle, an ancient philosopher whose theory was different. Galileo's findings were ignored by most people, and Aristotle's view was still accepted as correct until Isaac Newton proved Galileo was right. This also led to Newton creating his Law of Gravity.