Yours, Etc.: Origins and Uses of 8 Sign-Offs
1892 (n.) "adherent of populism;" 1893 (adj.), American English, from Latin populus "people" (see people (n.)) + -ist. Originally in reference to the U.S. Populist Party organized February 1892 to promote certain issues important to farmers and workers. The term outlasted the party, and by 1920s came to mean "representing the views of the masses" in a general way.