On an April morning in Manhattan last year, Steven Davis, the former chairman of the law firm of Dewey & LeBoeuf, reached for his ringing cell phone. He was sitting in the back seat of a taxi, on the way downtown to renew his passport. Dewey & LeBoeuf, which was often referred to in the press as a global “super firm,” was largely his creation. In 2007, he had engineered the merger of a profitable but staid midsized specialty firm—LeBoeuf, Lamb, Greene & MacRae—with a less profitable but much better-known firm, Dewey Ballantine. (Thomas E.