Who was Johannes Kepler, and why is he known today?

He was a German mathematician and astronomer who established a set of laws to describe planetary motion around the sun.

Johannes Kepler was the one that discovered three major laws of planetary motion, conventionally designated as follows: (1) the planets move in elliptical orbits with the Sun at one focus; (2) the time necessary to traverse any arc of a planetary orbit is proportional to the area of the sector between the central body and that arc (the "area law"); and (3) there is an exact relationship between the squares of the planets’ periodic times and the cubes of the radii of their orbits (the "harmonic law"). Kepler himself did not call these discoveries "laws," as would become customary after Isaac Newton derived them from a new and quite different set of general physical principles.