Wernher Magnus Maximilian Freiherr von Braun (23 March 1912–16 June 1977) was a German engineer and scientist. He worked as a rocket designer between the 1930s and 1970s. Some people say he was the most important rocket engineer of the 20th century. He worked for the Nazis during World War II. After World War II, he went to the United States. There, he worked for NASA. In 1955, ten years after entering the country, von Braun became a US citizen.