Mr. Gass’s admirers loved the layers of poetry and philosophy that kept them digging like archaeologists through the strata of Western intellectual thought. But his complex fiction lost many readers and caused some critics to accuse him of sacrificing character for literary gimmicks.

“Oddly enough I think of myself as more of a realist than most of the realists,” he told The New York Times in 1999. “In my books there’s darkness. You don’t know everything. In the Victorian novel, everything is clear; in the real world, motives are mixed. People are unreliable. There are contradictions. People forget. There are omissions. You certainly don’t know everything. There aren’t good people and bad people. There are shades of this and that.”

His masterwork was “The Tunnel” (1995), a 652-page novel in which the main character, the lonely, miserable and unlikable William Frederick Kohler, a middle-aged history professor at a Midwestern university, retreats to his basement, where he begins, little by little, to tunnel his way out — metaphorically trying to escape from a loveless marriage and a painfully unhappy life.

All the while, Kohler reflects on that life in a series of digressions as he struggles to write the preface to his magnum opus, a study of Nazi Germany. Mr. Gass said of his character: “This guy is either lying or he is forgetting or he isn’t getting things right. That’s what life is like.”

“The Tunnel” took Mr. Gass almost 30 years to finish but did not find much of an audience. And while many critics praised it effusively, others, had trouble with it.

“It will be years before we know what to make of it,” the poet Robert Kelly wrote in The New York Times Book Review, calling the book an “infuriating and offensive masterpiece.”

Image “The Tunnel” was once called an “infuriating and offensive masterpiece.” Credit... Knopf

William Howard Gass was born in Fargo, N.D., on July 30, 1924, the son of William Gass and the former Claire Sorenson. When he was six weeks old his father moved the family to Warren, Ohio. William grew up during the Depression, spending summers in North Dakota. “These were the dust bowl years, too; grasshoppers ate even the daylight,” he wrote.