The patriarch, Joseph P. Kennedy, spent a big part of his life in the movie business, so it's fitting, perhaps, to quote from a film as we reflect on the family he built. The Man Who Shot Liberty Valance opened in 1962, when John F. and Robert F. Kennedy ruled Washington and young Edward M. Kennedy was winning his first of nine U.S. Senate elections. It is the story of a decent, but entirely human, fellow whose fame doesn't quite match the ambiguous facts of history. And there comes a point when the myth assumes a reality all its own. "This is the West, sir," says a newspaper editor. "When the legend becomes fact, print the legend."

The Kennedy family saga is an epic tangle of true legends and legendary truths. The father, with his bottomless checkbook and flair for...