Joan Crawford - there are many reasons why. She was a woman with beauty and brains - who knew how to use both to her advantage. And she did so in a time when women, like children, were seldom heard, much less listened to. She was among those very few female Stars whose names and talent commanded top billing. And a great number of America's movie goers paid their admission just to see a film because Joan Crawford starred in it.
Whether or not she was a good parent, I'm not to judge. But she never lost her humility regarding who put her where she was - her fans and audience.