It became the key for “The Mitzvah” (“The Good Deed”), a short one-man play in which he has three roles: Christoph Rosenberg, a half-Jewish lieutenant in the German army, first encountered as he stands at attention during a mass tribute to Adolf Hitler in 1939; Schmuel Berkowicz, a Polish Jew from Bialystok, first seen begging for his life in Auschwitz; and The Chorus, a Groucho Marx-like comedian who interjects wry commentary.

As part of a tour, Mr. Grunwald will bring the play, and a related lecture based on his research, to Paramus, Franklin Lakes and Toms River in the coming days. Mr. Grunwald, who lives in Manhattan, wrote the play with Annie McGreevey, an actor, writer, director and teacher who lives in West New York and who became his director. They knew each other from acting class, both said in a joint telephone conversation. But it was after Mr. Grunwald helped Ms. McGreevey with her lines and saw her perform in “Rose,” a one-woman play by Martin Sherman in which she portrayed an 80-year-old Holocaust survivor, that he decided to visit his aunt.

In his original draft, Mr. Grunwald said, he injected into his portrait of Christoph, who does not consider himself Jewish, “a lot from my aunt, from some elements of my conversation with her,” including her own continuing pride in having been an assimilated German Jew.

That pride was shared by his mother, Mr. Grunwald said, and by many other German Jews. He added Schmuel Berkowicz to show some of what happened to Eastern European Jews. When he and Ms. McGreevey realized they needed some humorous leavening, “Annie came up with Groucho, a social critic, a sage, who in the play helps us digest the material,” he said.

Mr. Grunwald said he hoped the play, besides imparting some German and German-Jewish history, “engenders conversation about the nature of prejudice and identity.”