Mr. Toren’s campaign to recover the stolen works drew headlines when a painting by Max Liebermann, “Two Riders on the Beach, surfaced in the collection of Cornelius Gurlitt, an elderly recluse. Mr. Gurlitt had hoarded the art he inherited from his father, a dealer for the Nazis, in his homes in Munich and Salzburg. Mr. Toren had been searching for the painting for years.
Images of the work with other rediscovered paintings were displayed at a news conference given by the state prosecutor in Augsburg, Germany, in November 2013. By then Mr. Toren was blind, a consequence of a severe case of shingles, but he could remember last seeing the painting hanging in his great-uncle’s villa in Germany 75 years earlier — on Nov. 10, 1938, the day after Kristallnacht. The Gestapo eventually seized his great-uncle’s art collection, and “Two Riders” wound up in the hands of an unscrupulous museum director, who sold it to Mr. Gurlitt’s father.
“I always liked that painting because I liked horses,” Mr. Toren said in 2014. “I will get it back.”
And he did — finally — the next year, after a host of bureaucratic delays. Asked then if he felt a sense of closure, he responded with characteristic emphasis. “No!” he said. “We are looking for more important paintings” from his great-uncle’s collection.
The discovery of Mr. Gurlitt’s trove, which encompassed about 1,500 works by Claude Monet, Henri Matisse, Otto Dix and other artists, revived interest in the issue of Nazi-looted art. Mr. Toren was one of several heirs to claim that the collection held stolen works. Since its discovery, a total of 13 have been identified as looted and have been returned.
Klaus-Günther Tarnowski was born on April 30, 1925, and grew up with an elder brother in a well-to-do family in an elegant neighborhood of Breslau, now Wrocław, in Poland, but then part of Germany. (He changed his name after fleeing.) His father, Dr. Georg Martin Tarnowski, was a successful lawyer and the proud leader of the Breslau chapter of the Association of Jewish War Veterans. His mother was Maria (Friedmann) Tarnowski.
Georg Tarnowski’s first wife, who died during World War I, was a niece of the painter Lesser Ury, and the walls of the family apartment were adorned with the paintings she had received for every birthday.
“Two Riders on a Beach” (1901), by the German painter Max Liebermann. “I always liked that painting because I liked horses,” Mr. Toren said. “I will get it back.” He did.
At 10, after the Nazis had seized power, Klaus-Günther began attending the prestigious Zwinger Gymnasium, where he encountered anti-Semitism and bullying by teachers and pupils alike. His non-Jewish nanny was compelled to leave the household. In a 2014 interview, he recalled being heartbroken at having to give away his two pet parakeets, Habakkuk and Zephaniah. Breslau’s cinemas and ice cream parlors posted signs on their doors warning, “Jews Not Welcome.”
Kristallnacht remained etched in Mr. Toren’s memory 75 years later. He remembered watching unseen from the balcony with his parents as the Jewish-run liquor store below was plundered and bottles were smashed against the walls. The next morning, the Gestapo came for his father. After three weeks at Buchenwald, he was allowed to return home gaunt, his head shaved.
He managed to squeeze his son, now 14, onto what would prove to be the last Kindertransportevacuation to Sweden before World War II broke out. Mr. Toren left on Aug. 23, 1939, only days before Germany invaded Poland, and never saw his parents again. Both perished at Auschwitz.
In Sweden, Mr. Toren managed to track down a distant relative, who agreed to finance his tuition. He passed his exams and went on to study chemistry in Stockholm. In 1948, he was recruited by Haganah, a Zionist paramilitary organization later absorbed into the Israel Defense Forces, and he left for Israel.
Mr. Toren was born with a degenerative eye condition, retinitis pigmentosa. Discharged from the Israeli army because his eyesight was inadequate, he began working as a chemist, but found the work dull. He applied for a position in Tel Aviv as an assistant to a patent lawyer. In Israel he met Sarah Brown, an American social worker who later became a psychoanalyst, and they married in 1953. She died in 2019. In addition to his son, Mr. Toren is survived by two grandchildren.
After a brief spell in London, the couple moved to New York in 1955, and Mr. Toren took up night studies at New York Law School. After graduating in 1960, he, too, became a patent lawyer. As one of America’s top German-speakers in the field, he often attracted German companies as clients, many of whom had had strong Nazi connections.
"My father didn’t have any misgivings about representing clients like this because he felt that if he didn’t do the work, someone else would, and he deserved to profit financially,” Peter Toren said by email. “He also charged what he called the ‘Nazi premium,’ which was about 20 percent to 25 percent more than other clients. I don’t think this was listed in the billing statements.”
Mr. Toren contracted shingles in 2007; a devastating side effect was the complete loss of his eyesight within three days. After that, well into his 80s, he retired. In his last years the quest for his family’s stolen art became his preoccupation.
He sued Germany and the state of Bavaria in 2014 in federal court in Washington. The case, which is pending, aims to recover 54 of his great-uncle’s paintings whose location is unknown.
"We will continue to search for and hopefully locate additional works of art looted by the Nazis,” Peter Toren, also a lawyer, said. “My father would have expected no less.”