Charles Atlas, who sold thousands of "dynamic tension" resistance-training regiments from the 1930s through the 1960s with the comic strip ad, "The Insult that Made a Man out of Mac."
But few people, even bodybuilding aficionados, realize that before Charles Atlas, the mail-order muscle-building market was dominated by Earle E. Liederman (1886-1970), an associate of Eugen Sadow who advertised "Become a giant among men!" to the wimpy office boys of the Jazz Age.
The former physical education teacher, Vaudeville strongman, and professional acrobat began distributing his book, Muscle Development, in 1920, and continued with The Science of Wrestling and Secrets of Strength.
His lessons were typewritten, addressed personally to the student, and tailored to his/her individual needs (actually ghost-written by one of his army of assistants), with practical advice like "don't invest in many collars, as your neck size will increase dramatically."
One of his students, he claimed, was Charles Atlas himself. Liederman himself provided the illustrations, displaying a massive physique even in his fifties.
Joe Weider's new magazine, Muscle Power.
His column, "Let's Gossip," with its dish on the sun-and-surf hijinks of the glitterati, is credited with drawing hundreds of young muscle enthusiasts to L.A., where many posed for the gay-vague Physique Pictorial and were discovered by gay casting agent Henry Willson.
I don't know if he was gay. When you read his columns, he comes across as very fey, a drag queen Auntie, sweetie darling. But he was married to Miss Alaska for awhile, so I can't tell.
His course is still available online.