Marilyn was the very first playmate of the month which started in December or 1953. Wiki explains it best saying, “Playboy’s editor Hugh Hefner chose what he deemed the “sexiest” image, a previously unused nude study of Marilyn stretched with an upraised arm on a red velvet background from 1949.The heavy promotion centered around Marilyn’s nudity on the already famous calendar, together with the tease marketing, made the new Playboy magazine a success.”
In December 1953, 27-year-old Hugh Hefner published the very first Playboy magazine. This first edition of Playboy was 44-pages long and had no date on its cover because Hefner wasn’t sure there would be a second edition. In that first run, Hefner sold 54,175 copies of Playboy magazine at 50 cents each. The first edition sold so well because Marilyn Monroe was the “Sweetheart of the Month” (which was thereafter termed “playmate”).
On the front cover of the first edition of Playboy, Marilyn Monroe appeared waving her hand. Inside, Marilyn Monroe bared it all in the centerfold. (Monroe did not pose nude specifically for Playboy; Hefner had purchased the picture from a local printer who made calendars.)
This first edition of the magazine is also the only Playboy that does not have Hugh Hefner’s name inside.
On the first page, Hefner humorously wrote, “We want to make it clear from the very start, we aren’t a ‘family magazine.’ If you’re somebody’s sister, wife or mother-in-law and picked us up by mistake, please pass us along to the man in your life and get back to your Ladies Home Companion.”
Info from About.com
Marilyn in the Media 