Marilyn Monroe is the ultimate icon because of four reasons:
1.) She had a style characteristic of her era.
2.) She has an iconic, recognisable pose (the dress blowing up).
3.) She was controversial (affair with president, topless photos etc).
4.) She died young.
People are fascinated with her beauty because, unlike Elizabeth Taylor or Brigitte Bardot, we never saw her age. She'll always be a youthful, sexy character, forever, and it therefore death immortalises these famous figures.
But what if she never died? Would she be as iconic today if she was still alive, 88 years-old, and looked like this:
Would the tragic beauty element of her persona be lost? Or would she be like Audrey Hepburn, who grew old gracefully, died in her 60s and, despite this, is on a similar level of iconicness due to her fashion.