Friedrich Fehleisen (/ˈfeːlaɪ̯sən/) (1854–1924) was a German surgeon whose work focused on streptococcal bacteria. Dr. Fehleisen's work played a necessary role in the eventual uncovering of the etiology of many streptococcal illnesses. He made integral contributions to modern medicine's understanding of the Streptococcus pyogenes organism. He was born in Reutlingen, Württemberg, in 1854, and died in San Francisco, California, in 1924.