Caption: Alexander Friedmann (1888--1925): Russian-Soviet aviator, ballonist, mathematician, meteorologist, physicist, pioneering cosmologist, and discoverer of the eponymous Friedmann equation in 1922. See also Wikipedia: Alexander Friedmann, The MacTutor History of Mathematics archive: Aleksandr Aleksandrovich Friedmann, and Astronomer file: alexander_friedmann.html).

Credit/Permission: Anonymous photographer, before or circa 1925 / Public domain.
Image link: Wikipedia: File:Aleksandr_Fridman.
Local file: local link: alexander_friedmann_image2.html.
File: Astronomer file: alexander_friedmann_image2.html.