Sergei Ivanovich Zhegalov was a prominent geneticist and one of the founders of scientific plant-breeding in Russia. Beginning in 1922, he directed the breeding station at the K.A. Timiriazev Agricultural Academy in Moscow and also organized the Gribovo breeding station for work on vegetables. Zhegalov worked on the improvement of practically all cultivated plants and developed many new breeds of carrots, beans, oats, turnips, peas, and other cultures. He authored the first Russian textbook on plant selection based on modern genetics. This biographical article uses materials from the scientist's family archives, as well as recollections of his students and relatives.