While he did not invent the telescope, Galileo modified one of the devices before discovering a number of planets and moons, including Venus, which inspired a scientific revolution. His contention that Copernicus was correct about a heliocentric galaxy drew the ire of the Vatican, which believed the Earth was at the center of the galaxy. Galileo later published his findings, which resulted in his imprisonment.
Galileo was an undistinguished college teacher through his middle ages. It wasn't until he was 70 that he made waves with his theories on the structure of the galaxy.
Born in 1564 in Pisa, Galileo was an astronomer, mathematician, physicist and philosopher. He later became known as the father of modern observational astronomy, if not modern science in general, for his improvements to the telescope and subsequent research.
However, as a teacher, prior to his discoveries, he was required to teach the prevailing wisdom that dictated the Sun and other planets all revolved around Earth. His book, "Two Chief World Systems," resulted in his trial for and conviction of heresy. After being forced to recant his views on a heliocentric galaxy, he spent the remainder of his life under house arrest in his villa near Florence.