Marion S. Barry, Jr., the sharecropper's son and civil rights activist who became Washington, D.C.'s most flamboyant and divisive mayor for four terms, died early Sunday at the age of 78. United Medical Center spokeswoman Natalie Williams said Mr. Barry arrived at the hospital around 12:30 a.m. and died at 1:46 a.m., following a brief stay at Howard University Hospital.