Alexander Stepanovich Popov (March 16 – 1859 – January 13 – 1906) was a Russian physicist who along with Guglielmo Marconi was the first to communicate messages by radio waves.
In 1894 he built one of the first radio receivers, using a coherer, which he used as a lightning detector. On May 7, 1895, at the Russian Physical-Chemical Society, he demonstrated reception of radio signals from a transmitter. This day is celebrated in the Russian Federation as Radio Day. The paper on his findings was published the same year. On March 24, 1896, he demonstrated transmission of radio waves between different campus buildings in St Petersburg. He was also the first to use a wire aerial.