In 1938, Mormon missionaries from North America, under the leadership of Frederick Salem Williams, formed an athletic club, Club Atlético Los Mormones (‘The Mormons Athletic Club’, CALM), in Buenos Aires, Argentina. CALM would sponsor professional teams in baseball, softball, and basketball, all bearing the name Los Mormones (‘The Mormons’). Los Mormones won three league championships in the four years they played baseball and four championships in the five years they played softball. Two of their basketball players would become national all-stars, one of whom would represent Argentina at the South American Championship in 1940. Williams served as president of the softball league and vice president of the baseball league. Los Mormones’ story is outlined and situated in relation to the various discourses that, woven together, constitute the cultural context of modern Argentine sport: physical culture and modernity, United States-Argentine relations, amateurism versus professionalism, and the spread of North American sports to Latin America.