Dr. Leopold wrote several books on Schiele, including “Egon Schiele” (Phaidon), a large illustrated monograph published in this country in 1973.

Like many European art museums in recent years, the Leopold has confronted questions about the provenance of some of its artworks, specifically about whether they had been the property of European Jews who were either forced to flee without their possessions or died in the Holocaust.

In the late 1990s, two Schiele paintings from the Leopold collection attracted worldwide attention. At the time, the paintings were on display at the Museum of Modern Art in New York, and two Jewish families came forward to challenge the Leopold’s ownership of them.

Rudolf Leopold was born in Vienna on March 1, 1925. In interviews over the years he had said that his family opposed the Nazi regime; Mr. Pokorny said by e-mail on Tuesday that during the war Dr. Leopold avoided conscription by taking refuge in a small mountain village.

He earned his medical degree from the University of Vienna in 1953. Around this time, he became intensely interested in art. He began collecting the work of Schiele and others, which were then relatively inexpensive.

By 1994, Dr. Leopold owned a vast collection valued at more than $500 million. That year, in conjunction with the Austrian government, he established a public foundation. Under the terms of the arrangement, the government paid him about a third of the collection’s value and built the museum that houses it today.

In October 1997, “Egon Schiele: The Leopold Collection,” an exhibition of about 150 works, opened at the Modern. Before the year was out, the ownership of two paintings had been called into question. One, “Dead City III,” a townscape, was claimed by heirs of Fritz Grunbaum, a Viennese cabaret artist who died in Dachau.

The other, “Portrait of Wally,” was a painting of Schiele’s mistress, Valerie Neuzil, known as Wally. Heirs of its original owner, Lea Bondi Jaray, a Jewish art dealer who had fled Austria for London, claimed the painting belonged to them. (Ms. Jaray had died in 1969.)

In interviews, Dr. Leopold denied having knowingly dealt in looted art. “I’m not a Nazi and I’m not a Nazi profiteer,” he told The Jerusalem Report in 1998. “My family were totally against Hitler’s regime.”

Dr. Leopold is survived by his wife, Elisabeth; two sons, Rudolf Jr. and Diethard; a daughter, Gerda; a brother Günther; and four grandchildren

“Dead City III” was eventually returned to the Leopold Museum. Although Ms. Reif is no longer directly involved in the case, two other heirs of Mr. Grunbaum continue to contest ownership of the painting through the courts here and in Austria.

In a legal odyssey that continues to this day, “Portrait of Wally” has wended its way though state and federal courts here for more than a decade. A civil trial, intended to determine whether Dr. Leopold knew the painting was stolen when he sent it to the United States for exhibition in 1997, is scheduled to begin in Manhattan on July 26 at the United States District Court for the Southern District of New York.