title: Diode
context: About 20 years later, John Ambrose Fleming (scientific adviser to the Marconi Company and former Edison employee) realized that the Edison effect could be used as a radio detector. Fleming patented the first true thermionic diode, the Fleming valve, in Britain on November 16, 1904[13] (followed by  in November 1905).
question: Who developed the first diode?
answers: John Ambrose Fleming