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, said that he had learned late Sunday that Mr. Grass had been hospitalized after falling seriously ill very quickly. The cause of death was not announced.

Mr. Steidl said he drank his final schnapps with Mr. Grass eight days ago while they were working together on his most recent book, which he described as a “literary experiment” fusing poetry with prose. It is scheduled to be published in the summer.

“He was fully concentrated on his work until the last moment,” Mr. Steidl said.

Mr. Grass was hardly the only member of his generation who obscured the facts of his wartime life. But because he was a pre-eminent public intellectual who had pushed Germans to confront the ugly aspects of their history, his confession that he had falsified his own biography shocked readers and led some to view his life’s work in a different light.

Mr. Grass came under further scrutiny in 2012 after publishing a poem criticizing Israel for its hostile language toward Iran over its nuclear program. He expressed revulsion at the idea that Israel might be justified in attacking Iran over a perceived nuclear threat and said that such a prospect “endangers the already fragile world peace.”

The poem created an international controversy and prompted a personal attack from Prime Minister Benjamin Netanyahu. Mr. Grass later said that he had not meant to criticize the country, but only its government.

He was propelled to the forefront of postwar literature in 1959, with the publication of his wildly inventive masterpiece “The Tin Drum.” Critics hailed the audacious sweep of his literary imagination. A severed horse’s head swarming with hungry eels, a criminal hiding beneath a peasant woman’s layered skirts and a child who shatters windows with his high-pitched voice are among the memorable images that made “The Tin Drum” a worldwide triumph.

In awarding Mr. Grass the Nobel Prize in 1999, the Swedish Academy praised him for embracing “the enormous task of reviewing contemporary history by recalling the disavowed and the forgotten: the victims, losers and lies that people wanted to forget because they had once believed in them.” It called “The Tin Drum” “one of the enduring literary works of the 20th century.”

Mr. Grass was a playwright, essayist, short-story writer, poet, sculptor and printmaker as well as a novelist, but it was as a social critic that he gained the most notoriety, campaigning for disarmament and broad societal change.

But ultimately, his uncompromising antimilitarism and his warnings that a unified Germany might once again threaten world peace led some of his countrymen to criticize him as a pedantic moralist who had lost touch with real life.

He revealed his Nazi past himself, days before a memoir, “Peeling the Onion,” was to be published, bringing on accusations of hypocrisy. Mr. Grass had long said that he had been a “flakhelfer” during the war, one of many German youths pressed to serve in relatively innocent jobs like guarding antiaircraft batteries. But in an interview with the newspaper Frankfurter Allgemeine, he admitted that he had been a member of the elite Waffen-SS, which had perpetrated horrific crimes. By then some knew that he had understated his role during the war, but the specific information came as a shock.

“It was a weight on me,” Mr. Grass, then 78, said. “My silence over all these years is one of the reasons I wrote the book. It had to come out in the end.”

In the memoir, he reflected on the vagaries of conscience and memory. “What I had accepted with stupid pride of youth I wanted to conceal after the war out of a recurrent sense of shame,” he wrote. “But the burden remained, and no one could lighten it.”

Although he was conscripted into the SS in 1944, near the end of the war, and was never accused of atrocities, the fact that he had obscured this crucial part of his background while flagellating his fellow Germans for cowardice set off cries of outrage.

Detractors and Defenders

“Moral suicide,” the newspaper Welt am Sonntag said. The playwright Rolf Hochhuth said it was “disgusting” that Mr. Grass had denounced President Ronald Reagan and Chancellor Helmut Kohl for their 1985 visit to a cemetery in Bitburg where Waffen-SS soldiers were buried, while hiding the fact that he had been in the SS.

Mr. Grass’s defenders argued that his social and political influence had forced Germany to face its Nazi past and atone for it. He might not have been able to play that role, they said, if he had been forthright about his background.

With his mane of black hair and drooping walrus mustache, bifocals slipping down his nose and smoke curling from his pipe, Mr. Grass was almost a caricature of the postwar European intellectual. His books were all but inseparable from his public persona, giving him a unique position in German life for more than half a century.

“The Tin Drum” became one of the most widely read modern European novels. It also made Mr. Grass a leading spokesman for a generation barely old enough to have recalled or participated in Nazi crimes.

The book’s hero, Oskar Matzerath, possessing the mind of an adult, wills himself at the age of 3 to stop growing. Thereafter he expresses himself only by pounding one of many toy tin drums he carries constantly and shrieking so piercingly at important moments that his voice shatters glass.

As the book unfolds, the Nazi army invades Poland, and later is pushed out by the Soviets. Oskar discovers odd forms of sexuality, joins a company of dwarfs who entertain German troops, and becomes an engraver of tombstones. After the war he joins a jazz band, but decides on a quieter life. He allows himself to be convicted of a murder he did not commit, is judged insane and committed to an institution, where he writes the memoir that becomes “The Tin Drum.”

Oskar was viewed as representing a German nation so morally stunted that it could not find the courage to prevent Nazism.

At one point in “The Tin Drum” Mr. Grass writes: “There was once a grocer who closed his store one day in November, because something was doing in town; taking his son Oskar by the hand, he boarded a Number 5 streetcar and rode to the Langasser Gate, because there as in Zoppot and Langfuhr the synagogue was on fire. The synagogue had almost burned down and the firemen were looking on, taking care that the flames should not spread to other buildings. Outside the wrecked synagogue, men in uniform and others in civilian clothes piled up books, ritual objects and strange kinds of cloth. The mound was set on fire and the grocer took advantage of the opportunity to warm his fingers and his feelings over the public blaze.”

Symbols of Weakness

An intense antinationalist, Mr. Grass viewed his country with emotions that could flare into fear and hatred. Some critics said that the purposely small and weak Oskar symbolized what Mr. Grass wanted for Germany.

In the 1960s and ’70s, much of Mr. Grass’s work dealt with the German themes of disillusionment, the militaristic past and the challenges of building a post-Nazi society.

His greatest successes of the period were “Cat and Mouse” (1961), about a man whose unusually large Adam’s apple forever sets him apart from the rest of humanity, and the Joycean “Dog Years” (1963), which analyzes three decades of German history and suggests that the country has not progressed much. These novels, along with “The Tin Drum,” make up what Mr. Grass called his “Danzig Trilogy.”

While he was writing these works, Mr. Grass also campaigned and wrote speeches for Willy Brandt, who was one of West Germany’s dominant politicians from 1957, when he was elected mayor of Berlin, to 1974, when he stepped down after five years as the country’s first Social Democratic chancellor.

Mr. Grass later demonstrated against the deployment of American nuclear missiles in Germany, denounced the German arms industry and quit the Social Democratic Party, the Berlin Academy of Arts and the Lutheran Church. He called the Lutheran and the Catholic hierarchies “moral accomplices” of Nazism.

He was a tireless defender of Fidel Castro’s Cuba and embraced Nicaragua’s left-oriented Sandinista government in the 1980s. Yet he described himself as an opponent of revolution.

He denounced repression in Soviet-bloc countries and attacked governments run by religious fundamentalists, but his criticism was often accompanied by denunciations of Western, and especially German, capitalism. In opposing the first Persian Gulf war, for example, he focused his anger on his own country, accusing German companies of arming the Iraqi dictator Saddam Hussein.

“Once again, it is Germans who are designing and producing poison gas factories,” he said in an interview. “This is where you really see the German danger. It isn’t nationalism, and it isn’t reawakened neo-Nazis. It is simply the unchecked lust for profit.”

Many of Mr. Grass’s books are phantasmagorical mixtures of fact and fantasy, some of them inviting comparison with the Latin American style known as magical realism. His own name for this style was “broadened reality.”

“Günter Grass’s books present surprising and extremely contradictory combinations of opposites,” the Russian-German writer Lev Kopelev wrote in an essay on the occasion of Mr. Grass’s 65th birthday. “Minutely detailed presentations of real things and scientifically precise descriptions of historical events are melted together with fairy tales, legends, myths, fables, poems and wild fantasies to produce his own special poetical world.”

Mr. Grass was renowned for his wide-ranging tastes. He was an epicure who favored hearty peasant food, and his work carries the aroma of home-cooked dishes like smoked goose breast and roast pork with sauerkraut and caraway seeds.

His fascination with animals was reflected in book titles like “The Flounder” and “From the Diary of a Snail.” He was a jazz lover, once worked as a jazz musician, and collaborated on “O Susanna,” an illustrated book on jazz, blues and gospel music published in 1959.

Some critics hoped Mr. Grass would produce a monumental novel encompassing all the great themes that have tormented Germany through its history, and felt betrayed when he did not. Many of his later works were met with both critical and popular indifference.

The dominant German literary critic during most of Mr. Grass’s career, Marcel Reich-Ranicki, who died in 2013, called him “greatly overrated.” Mr. Reich-Ranicki once appeared on the cover of the magazine Der Spiegel ripping apart a copy of a Grass book he especially loathed, “Too Far Afield,” a 1995 novel centered on two men in their early 70s roaming Berlin after the fall of the Berlin Wall as they ponder Germany’s past and present.

After the wall was breached in 1989, Mr. Grass argued against German unification on the ground that a people responsible for the Holocaust had forfeited the right to live together in one nation. He suggested that East and West Germany remain separate for a time and then join a loose confederation of German-speaking states.

“Auschwitz speaks against even a right to self-determination that is enjoyed by all other peoples, because one of the preconditions for the horror, besides other, older urges, was a strong and united Germany,” he said in a 1990 speech. “We cannot get by Auschwitz. We should not even try, as great as the temptation is, because Auschwitz belongs to us, is branded into our history, and — to our benefit! — has made possible an insight that could be summarized as, ‘Now we finally know ourselves.’ ”

A Character as a Nation

Günter Wilhelm Grass came of age on a continent torn by hatred. He was born in Danzig on Oct. 16, 1927, to a German father and a mother who was a Kashubian, a Slavic ethnic group with its own language and traditions. Danzig, now the Polish city of Gdansk, was then a free city under the control of the League of Nations, but its population was loyal to the Reich. It was the first territory seized by the Nazis.

The author and critic Morris Dickstein wrote of the city: “One of the world’s most frequently besieged and contested cities (as Mr. Grass loves to emphasize), Danzig during the 1930s was a symbol of Germany’s lost territories and a focus of Nazi agitation. By the end of the war it was buried in rubble with all its German population driven out. It is a truism to say that except for Southerners like Faulkner, who inherited the consequences of the Civil War, American writers have a relatively undeveloped sense of history. But even among Europeans, Mr. Grass was well situated to learn how history buffets and battles local dreams and individual lives.”

Günter joined the Nazi children’s organization Jungvolk at the age of 10. Like many Germans of his generation, he later claimed to have done no real service to the Nazi war effort.

Among them was Joseph Ratzinger, who went on to become Pope Benedict XVI. After the war ended, Mr. Grass and the future pope were prisoners together in an Allied camp at Bad Aibling. Mr. Grass later remembered Mr. Ratzinger as “extremely Catholic” and “a little uptight,” but “a nice guy.”

After returning to civilian life, Mr. Grass was drawn to art and poetry. He joined a loose but influential circle of critical intellectuals known as Group 47. Encouraged by other members, among them the writers Heinrich Böll and Uwe Johnson, he decided to abandon what some said was a promising career in sculpture and devote himself to literature.

Mr. Grass lived in Paris during the late 1950s and wrote “The Tin Drum” in a basement apartment there. It earned him worldwide acclaim, as well as accusations of blasphemy and pornography in Germany. Some said he was irresponsible to use a stunted child to represent victims of Nazism. Others were put off by the child’s ability to escape the doom the Nazis had decreed for the physically handicapped, and by his seeming misunderstanding of rape by soldiers as a gift to lonely women. Twisted sexual relationships wind through the book.

The book was banned in Communist countries, including Poland, meaning that it could not legally be read in Gdansk, the city where it was set.

“The Tin Drum’s” fame grew after the director Volker Schlöndorff made it into a vivid movie, which won the 1979 Academy Award for best foreign language film.

Some critics found his increasingly apocalyptic books published after the 1970s repetitive and self-righteous. Others said his relentless activism had overwhelmed his identity as a writer.

“Here is a novelist who has gone so public he can’t be bothered to write a novel,” John Updike wrote. “He just sends dispatches to his readers from the front line of his engagement.”

Mr. Grass’s marriage in 1954 to Anna Margareta Schwarz, a Swiss dancer, ended in divorce in 1978. He is survived by his second wife, Ute Grunert, an organist; four children from his first marriage, Laura, Bruno, Franz and Raoul; two stepsons from his second marriage, Malte and Hans; two other children, Helene and Nele; and 18 grandchildren.

Mr. Grass found defenders among his American friends, including the novelist John Irving, who assailed the dismantling of Mr. Grass’s reputation “from the cowardly standpoint of hindsight.”

“You remain a hero to me, both as a writer and a moral compass,” Mr. Irving wrote, adding that Mr. Grass’s courage was heightened by the truth. Mr. Grass said he was “not a pessimist, but a skeptic.” He rejected the view that artists should create rather than agitate. That, he said, leads to self-censorship that delights “the powers of church and state.”

Yet he said he rued the years in which he did not speak the full truth about himself. “The brief inscription meant for me reads: ‘I kept silent,’ ” Mr. Grass wrote in his memoir.

Why was he attracted to the SS?

“It was the newsreels,” he concluded. “I was a pushover for the prettified black-and-white ‘truth’ they served up.”

Melissa Eddy contributed reporting from Berlin.