Who was originally going to direct Apocalypse Now?

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I remember hearing my parents speak of 1979's "Apocalypse Now" in hushed tones. It was so dangerous that I wasn't allowed to watch it, but so good that I would definitely HAVE to watch it once I was old enough.

Being plagued by production issues, Martin Sheen nearly dying, and being based on a book called "Heart of Darkness" only helped to increase its allure.

It's also one of the reasons (just one, don't freak out on me) why Francis Ford Coppola is often cited as one of the best directors to ever get behind the camera. But he wasn't originally supposed to be the director. Who was?