Jimmy Savile is entirely unknown to Americans. Which is as it should be. He was a British disc jockey and children's-TV host, but, even by the debased standards of those callings, he didn't appear to have any particular talent. Yet, for half a century, until his death a year ago, he was one of the BBC's biggest stars: He hosted the first edition of Top of the Pops on TV in 1964, and he was there for the last in 2006. He had no discernible interest in pop music, but for millions of Britons his radio show was the accompaniment...