It's tough to imagine science without Galileo's contributions, as evidenced by this terrific reel of nicknames: "The Father of Science," "The Father of Modern Physics," and "The Father of Observational Astronomy." By vastly improving telescopes, Galileo was able to discover the phases of Venus, pick out the largest moons of Jupiter, and help prove that the solar system is heliocentric. His physics research laid the groundwork for the study of motion. On top of that, he survived an inquisition for discounting geocentric theories of the solar system.
(13) Stephen Hawking
Despite his struggle with ALS, Hawking is undoubtedly the only living theoretical physicist who's also a household name. His resume speaks for itself: Cambridge professor, black hole de-mystifier, author of crossover science hit A Brief History of Time, and all-around quantum gravity guru. Plus, he's got comedy chops; he's made appearances on The Simpsons, Futurama, and Conan.
Without Galileo, Hawking's contributions to cosmology would never have been possible. Hawking, though, took the field to places Galileo never could have imagined. Both overcame huge hurdles in creating their brilliant works, but which one's the bigger star?
[See the whole bracket here.]