Harry Grindell Matthews was an English inventor who claimed to have invented a death ray in the 1920s.

The death ray or death beam was a theoretical particle beam or electromagnetic weapon first theorized around the 1920s and 1930s. Around that time, notable inventors such as Guglielmo Marconi, Nikola Tesla, Harry Grindell Matthews, Edwin R. Scott, Erich Graichen and others claimed to have invented it independently. In 1957, the National Inventors Council was still issuing lists of needed military inventions that included a death ray.