Günter Grass, the German novelist, social critic and Nobel Prize winner whom many called his country’s moral conscience but who stunned Europe when he revealed in 2006 that he had been a member of the Waffen-SS during World War II, died on Monday in the northern German city of Lübeck, which had been his home for decades. He was 87. His longtime publisher, Gerhard Steidl, told reporters that he learned late Sunday that Mr. Grass had been hospitalized after falling seriously ill very quickly. The cause of death was not announced.