Few Hollywood stars of the 1950s and 1960s were so compelling, so utterly unique, that they actually came to define the era in which they worked and played. Marilyn Monroe was one of those stars.

From her earliest days as an actress until late in her career — when she had, against her will, been cast in the public eye as the century’s ultimate Sex Goddess — Marilyn posed for LIFE magazine’s photographers. Many of those pictures never ran in the magazine — and, in fact, were never published anywhere. This gallery changes all that.

The negatives for the revelatory images seen here were discovered during the years-long effort to digitize LIFE’s immense, storied photo archive — an archive that includes outtakes and entire photo shoots that, for reasons as varied as the subjects they covered, were never published.

Here, then, is a series of stunning shots of the one and only Marilyn, as well as some possible explanations why they never made it into print.