At the age of 41 (he turns 42 on Saturday), Mr. Coates has become one of the most influential black intellectuals of his generation, joining predecessors including Ms. Morrison, Professor Henry Louis Gates Jr., and Dr. Cornel West. “He’s a rock star,” said Dr. Nell Irvin Painter, professor emeritus of American history at Princeton University, adding that Mr. Coates is asking questions that even “other historians have not been asking.”