Ole Romer was a Danish astronomer who lived from 1644-1710. He is most well known for being the first to make quantitative measurements of the speed of light, which he did in 1676. 

Romer was a professor of astronomy at the University of Copenhagen for nearly thirty years. He was also royal mathematician, and in this position he introduced the first national system of weights and measures and convinced the king to introduce the Georgian calendar in Denmark-Norway. Romer also invented one of the first thermometers and temperature scales - which was later improved upon by Fahrenheit - created increasingly accurate celestial maps, invented the first street lights used in Denmark, and established several navigation schools.