Who they were
Galileo Galilei was an Italian astronomer, physicist, and mathematician, a central figure of the Scientific Revolution.
What they did
He improved the telescope and observed the moons of Jupiter, the phases of Venus, and lunar craters, supporting Copernican heliocentrism; his advocacy led the Roman Inquisition to try him in 1633, forcing him to recant and spend his last years under house arrest. He also advanced the study of motion.
Legacy
Often called the father of modern observational astronomy and of modern physics, he became a symbol of the conflict between science and dogma, and the Church acknowledged errors in his condemnation only centuries later.