The two men who designed and built ENIAC were John Presper Eckert and John Mauchly. They built it from 1943 to 1945 at the University of Pennsylvania Moore School of Electrical Engineering.
What made ENIAC unique among other early computers is that it could be reprogrammed to perform different operations; contemporary devices were designed to perform only one program. It was funded by the Army to calculate ballistic trajectories for artillery shells, but World War II ended before it could perform once. Instead, its first calculations were used in top-secret evaluations of thermonuclear chain reactions. It was unveiled to the public in February of 1946.