Charles Atlas
Name at birth: Angelo Siciliano
For much of the 20th century Charles Atlas was America's most famous muscle man. Atlas immigrated from Italy as a boy, and in his teens he built up his physique using a system of bodybuilding which he later dubbed "Dynamic Tension." In 1928 he met businessman Charles Roman; the two men founded Charles Atlas, Ltd. and began selling bodybuilding courses by mail. Atlas advertisements appeared in comic books and magazines and made Atlas into a pop culture icon; his most famous ad, a cartoon in which a scrawny young man resolves to bulk up after a bully kicks sand in his face, ran for years. (Atlas also popularized the phrase "97-pound weakling.") The company was a great success and continued on after Atlas's death in 1972.
Extra credit: Atlas won a "Most Perfectly Developed Man" contest at Madison Square Garden in 1922, and continued to use the title the rest of his life... Atlas is no relation to the late 20th century electronic artist of the same name.
Other famous muscle men on Who2 include Arnold Schwarzenegger and Hercules.