Galileo Galilei was an Italian astronomer, physicist, and mathematician who played a crucial role in the Scientific Revolution. He is best known for his improvements to the telescope and his astronomical observations, which included the discovery of the four largest moons of Jupiter and the phases of Venus. His work laid the foundation for modern physics and astronomy. Galileo's advocacy for the Copernican system, which posited that the Earth revolves around the Sun, brought him into conflict with the Catholic Church. Despite facing opposition and being placed under house arrest, his contributions to science remain influential, earning him the title of the 'father of modern observational astronomy.'