Karl Ferdinand Braun (June 6, 1850 - April 20, 1918) was a German physicist.
Born in Fulda. Educated at the University of Marburg and the University of Berlin, receiving his Ph.D. in 1872. In 1874 he discovered the point-contact rectifier effect. He became director of the Physical Institute and professor of physics at Strasbourg in 1895. In 1897 he built the first cathode-ray tube oscilloscope, the CRT is still called the "Braun tube" in the german speaking countries. He also worked on wireless telegraphy from 1898, inventing the crystal rectifier and Guglielmo Marconi admitted to 'borrowing' from Braun's patents. In 1909 Braun shared the Nobel Prize for physics with Marconi for "contributions to the development of wireless telegraphy."
Braun went to America at the beginning of WWI to help defend the german wireless station at Sayville against legal attacks by the british Marconi Corporation. He died in his house in Brooklyn before the war ended in 1918.