Forget the aging, obese Orson Welles, who promised to "sell no wine before its time" on television in the 1970s and ’80s. This biography begins with the golden, whirling days of Welles’s early career, when the handsome boy out of Kenosha, Wisconsin, had boundless creative vitality— and the power to charm anyone, in the theater or out. In 1931, the 16-year-old Welles was appearing at the Gate Theater in Dublin. In 1935, he was staging a sensational Macbeth with black actors in Harlem. Two years later, he was directing and starring in Doctor Faustus, working with John Houseman and Marc Blitzstein on the inflammatory prolabor musical The Cradle Will Rock, and lending his plummy voice to the radio role of Lamont Cranston in The Shadow. Welles (and Houseman) launched the Mercury Theater with a revelatory Julius Caesar. When the Mercury began a weekly radio series in 1938, Welles hoodwinked the nation with War of the Worlds, his notorious fake news broadcast of a Martian invasion.

Then Welles invaded Hollywood, where he directed a first feature that many regard as the best film ever made by an American: Citizen Kane (1941). He went on to make a second, darker movie, The Magnificent Ambersons (1942), that might have been even greater had it been released in the form Welles intended. But he was in Brazil spending—wasting?—RKO’s money on a new film (which he left incomplete) when the studio edited 40 minutes out of Ambersons to give it more box office appeal. It was not the last time Welles would let a project slip out of his control—and in so doing seem to disavow what he had created.

The cliché about Welles is that everything went downhill after these first two films. But as Thomson, an actor and the author of several books about film, makes clear, this was not so—except in the sense that Welles never surpassed Kane. (But then, who has?) To be sure, Welles was forever beginning projects, dropping them, and taking them up again years later in makeshift locales and even with different casts. Yet despite a professional life that often resembled a Ponzi scheme, Welles the charlatan was also a practicing magician, reaching into his shabby hat and pulling out movie treasures such as Macbeth (1948), Touch of Evil (1958), The Trial (1962), parts of his admittedly disjointed Falstaff saga, Chimes at Midnight (1966), The Immortal Story (1968), and F Is for Fake (1973).

Thomson’s Welles is monumentally imperfect, full of passion, appetite, guile, lies, manipulation, misjudgment, arrogance, doubt, and, of course, a kind of genius. He is a manic-depressive egotist, "vividly disturbed and hysterically well, beyond treatment, so knowing that no doctor ever had a chance with him." This book traces the arc of his tumultuous life with surprising and admirable dispatch.

Too bad, then, that Thomson keeps intruding. His memory of seeing Citizen Kane for the first time, as a teenager alone in a revival house in London, is typical of the missteps: "I struggled with Kane because I knew that its show was more intense than anything I had seen, because I felt aroused by the need to run a little faster, because the shining young Kane was so entrancing."

Even more irksome are the imaginary dialogues between Thomson and—whom? his publisher? his alter ego?—that occur at irregular intervals without so much as a caveat lector. These are meant to dangle qualifications, questions, and alternative interpretations before our wondering eyes, and in their general fruitiness they are perhaps echt-Wellesian (the hokum Welles, that is). But mostly these dialogues recall the moments you faced as a child when a movie turned "icky" and you went to buy popcorn, hoping the actors would return to their senses by the time you returned to your seat. Too bad Thomson can’t resist trying to upstage his subject. He of all people should have realized that no one ever upstaged Orson Welles.