William Styron, the novelist from the American South whose explorations of difficult historical and moral questions earned him a place among the leading literary figures of the post-World War II generation, died today in Martha’s Vineyard, Mass., where he had a home. He was 81. The cause was pneumonia, coming after many years of illness, his daughter Alexandra Styron said. Mr. Styron’s early work, including “Lie Down in Darkness,” won him wide recognition as a voice of the South and the heir to William Faulkner. In subsequent fiction, like the critical and commercial success “Sophie’s Choice,” he transcended his background...