Jack Parsons (1914 - 1952) was a rocket engineer, chemist, and occultist. He founded both Jet Propulsion Laboratory and the Aerojet Engineering Corporation and invented the first rocket engine to use a castable, composite propellant.
Parsons was also a Thelemite attached to the Agape Lodge of the Ordo Templi Orientis, and in 1942 at the bidding of Aleister Crowley, became its leader. His association with the O.T.O. resulted in his expulsion from JPL and Aerojet in 1944.
Parsons partnered with L. Ron Hubbard of Scientology fame (or as some would say, "infamy") to conduct the Babalon Working, a series of rituals to invoke the goddess Babalon. Parsons left his wife for her sister Sara, who in turn, left Parsons for Hubbard. Hubbard and Sara went on to defraud Parsons of his life savings, whereupon he resigned from the O.T.O. an became a consultant for Israel's rocket program.
At the age of 37, Parsons died in a laboratory explosion which some say was suicide, and others murder. Today, Parsons is considered to be among the most important figures in the history of the United States Space Program, as well as one of the most significant figures in propagating Thelema across North America.