Orson Welles arrived in Hollywood as a boy genius, became a legend with a single perfect film, and then spent the next forty years floundering. But Welles floundered so variously, ingeniously, and extravagantly that he turned failure into "a sustaining tragedy"--his thing, his song. Now the prodigal genius of the American cinema finally has the biographer he deserves. For, as anyone who has read his novels and criticism knows, David Thomson is one of our most perceptive and splendidly opinionated writers on film.