German-Romanian physicist and engineer Hermann Oberth is one of the three founding fathers of modern astronautics, alongside Tsiolkovsky and Goddard. Born in Hermannstadt (now Sibiu, Romania), he developed a rigorous theory of reaction-based spaceflight as a teenager. His rejected doctoral thesis was published in 1923 as Die Rakete zu den Planetenräumen, a foundational text that inspired the first generation of space pioneers. He served as president of the Verein für Raumschiffahrt (VfR) and became Wernher von Braun's mentor. A consultant at Peenemünde during World War II, then an advisor to NASA in the 1950s–1960s, he witnessed the Apollo 11 launch at age 75. He died in Nuremberg in 1989, having devoted his entire life to the cause of spaceflight.