Galileo's full name is Galileo Galilei. He was an Italian mathematician who is well known for his significant work in laying the foundation for modern physics and astronomy.
Galileo made many discoveries in his lifetime. These discoveries included Jupiter's revolving moons, Venus' moon-like phases, the moon as a sphere instead of a flat circle and many others. One of his most renowned discoveries was proving true the Copernican theory that the earth revolved around the sun instead of the universe revolving around the earth. Though now accepted as common knowledge, this discovery caused great controversy against Galileo because it went against the doctrine of Aristotle and the order established by the Catholic Church.