It's not a single person who "says" things fall down due to gravity. It's a fundamental law of physics discovered and explained by many brilliant minds over centuries!

Here's a breakdown:

* Ancient Greeks: Philosophers like Aristotle observed objects falling and theorized about their movement, but didn't pinpoint gravity as the cause.

* Sir Isaac Newton (1643-1727): Newton formulated the Law of Universal Gravitation. He stated that every object in the universe attracts every other object with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers. This explained why things fall to Earth!

* Albert Einstein (1879-1955): Einstein's theory of General Relativity further explained gravity as a curvature in spacetime caused by mass and energy. This theory refined our understanding of gravity, especially in extreme situations like near black holes.

So, while Newton is often credited with the "discovery" of gravity, the understanding of gravity has evolved and been refined by many brilliant physicists over time.