He was an egotistical, big-mouthed womanizer who rose to become one of the most popular men in the world. He was born Cassius Marcellus Clay, became boxing’s heavyweight champion of the world and then, as Muhammad Ali, became one of the most controversial figures in America — and one of its greatest heroes.And now, his life and career have been depicted in Ken Burns’ four-part, eight-hour documentary “Muhammad Ali,” available on demand on PBS.Don’t miss it. And better yet, make certain your children have an opportunity …