Vera Florence Cooper Rubin (1928-2016) was an American astronomer whose work provided clear, observational evidence of the existence of dark matter. Rubin graduated with a degree in astronomy from Vassar College in 1948, completed a master's degree from Cornell University in 1951, and a Ph.D. from Georgetown University in 1954. In the 1960s, Rubin began what would become a life-long quest to understand the motions of stars within galaxies and the motions of galaxies themselves. Expecting to discover that stars farther from the center of a galaxy moved more slowly than stars closer to the center, Rubin instead observed that the outermost stars all seemed to be orbiting faster than they should. The stars were being influenced by the gravity of a vast amount of undetected mass surrounding the galaxy that came to be known as dark matter. Rubin collaborated with gifted instrument-maker W. Kent Ford, Jr. using an image tube spectrograph he developed at the Carnegie Institution of Washington. When Rubin used this instrument in telescopes it allowed for much more sensitive observations of distant galaxies than had previously been possible. These observations yielded evidence for the existence of dark matter that stimulated general acknowledgement that it forms much of the mass in the universe. For her ground-breaking work, Vera Rubin became the second woman in history to receive the prestigious Gold Medal of England's Royal Astronomical Society. Rubin was also a member of the National Academy of Sciences and was awarded the National Medal of Science in 1993.