Robert Goddard was the first person to fire a liquid fuelled rocket into space. He studied theories into rocket propulsion and conducted experiments to put his findings into practice. He calculated what it would take to put a rocket on the moon. He engineered several rockets for various rocketry programs.
Hermann Oberth engineered rockets and invented many ideas for rockets getting into space. He wanted to send rockets into the far reaches of space. He also managed to popularise the rocket idea through a film called ‘Woman in Space.’ He influenced students such as von Braun who went on to use both scientist’s ideas in future rockets.
Goddard was the first person to launch a liquid fuelled rocket but Oberth refined his ideas, recommended improvements and other inventions related to rockets. Both men had their ideas used by von Braun in prominent rockets such as the A-1 and A-2 rockets. Goddard is believed to have influenced Oberth in his main ideas.

http://en.wikipedia.org/wiki/Robert_Goddard_(scientist) Robert H. Goddard - Wikipedia, the free encyclopedia
http://en.wikipedia.org/wiki/Hermann_Oberth Hermann Oberth - Wikipedia, the free encyclopedia