Any time Carl Sagan holds someone in high regard, you know this person must be exceptional. One such person is Robert H. Goddard.
Most people have never even heard of this man, but he can easily be compared to the likes of Leonardo da Vinci and Nikola Tesla. In short, Goddard is singlehandedly responsible for the development of rocket science.
The sad thing is he was way ahead of his time and thus was ridiculed when he first presented his ideas. It was not until after his death that he was appreciated for what he had truly accomplished.
When he first proposed in 1919 that traveling to the moon in a rocket propelled vehicle was possible, almost all major newspapers and magazines criticized him for even thinking of such a preposterous idea. Everyone "knew" at the time it was impossible to travel through space, since there was no atmosphere to push against.
Goddard was not discouraged. Instead, he devoted himself to accomplishing his goal. For the next two decades, he worked tirelessly (and usually alone) to make space travel possible.
Carl Sagan wrote about Goddard in his book "The Dragons of Eden", page 88.
Read more about this fascinating individual at: Wikipedia