The German astronomer reputed to have sold his soul to the devil was Johann Faust. However, there is no historical evidence to support this claim, and it is likely a legend that developed over time. Faust is known for his research in astronomy and was the author of several works on astrology and the movements of the planets. He lived in the early 16th century and was a contemporary of other notable astronomers such as Copernicus and Kepler. Despite the legendary tale, Faust's contributions to the field of astronomy have been recognized and appreciated by scholars for centuries.