Story highlights Grass tried in his literature to come to grips with World War II and the Nazi era

His characters were the downtrodden, and his style slipped into the surreal

He stoked controversy with his admission to being a member of the Waffen SS

(CNN) Nobel literature laureate Guenter Grass, best known around the world for his novel "The Tin Drum," has died, his publisher said Monday. He was 87.

Grass died in a clinic in the city of Luebeck, where he was taken over the weekend, said Steidl publishing spokeswoman Claudia Glenewinkel. German media are reporting he died of pneumonia.

Grass focused in much of his work on learning from the horror of war and genocide by exploring motifs from his childhood city of Danzig, which is now Gdansk, Poland.

During the Nazi era, ethnic Poles and Jews were persecuted and deported from the multicultural city, at a time when they faced the possibility of mass murder.

"In his excavation of the past, Günter Grass goes deeper than most and he unearths the intertwined roots of good and evil," the Nobel committee wrote, when it awarded him the literature prize in 1999.