Michael Ottokar Popper, who had a doctorate in law, left the Jewish community in 1888 and converted to the Catholic faith. His wife Maria Franziska, born in 1889, to whom he had been married since 1922, was also a member of the Roman Catholic Church. Their son Otto Michael Popper was born on 6 October 1915. Until his retirement, Michael Ottokar Popper was the central director of the Clam-Gallas estate administration and was a member of the boards of directors of various companies. Contacts between the Popper couple and the Museum für Völkerkunde (MVK, now the Weltmuseum Wien) had existed since the early 1930s. In 1931, the museum purchased a Papuan breast ornament from Popper and, in the period up to the "Anschluss", repeatedly took on loans and objects for possible later purchase, such as a collection of ancient Peruvian objects in 1935. Some of the loans were returned before 1938.

According to the Nazi definition, the marriage of Michael Ottokar and Maria Popper was considered a "mixed marriage". On 28 August 1939, Maria Popper requested the return of the ethnographic objects that had not been purchased by the MVK until then. Two years later, she approached the museum again, this time with the request that it purchase the returned loans for RM 1,000, and sent a list of her collection of several dozen South and Central American objects. The MVK had the objects collected from Popper on 27 November 1941 but was ultimately interested in only 19 objects – ancient Peruvian ceramics and a stone spearhead – for which it paid RM 300. The acquisition was entered in the entry book under Post XV/1941, the MVK returned the remaining ethnographic artefacts to Maria Popper. Michael Ottokar Popper died in Vienna in April 1942, and was initially buried in the Jewish section of the Central Cemetery; in 1967 his body was exhumed and transferred to the so-called "Feuerhalle", a crematorium with an urn cemetery which is located across the street from the Central Cemetery in Simmering. Michael Ottokar Popper's son, Otto Michael Popper, a doctor of law, had fled to Milan in May 1940 but returned to Vienna twice. After Italy's capitulation and the German invasion, he was arrested during an attempted border crossing in 1943 and held for seven months in San Vittore prison in Milan, where he acted as an interpreter and worked for the resistance movement. The German occupying forces transferred him to the Fossoli police detention and transit camp near Carpi, close to Modena, which was taken over by the SS at the beginning of March 1944 and he was subsequently moved to the Bolzano-Gries transit camp in the summer as the Allies approached. With the first large transport at the beginning of August 1944, Otto Michael Popper was deported to the Mauthausen concentration camp and a month later to the Linz III satellite camp, where he was employed as an assistant clerk and died on 25 October 1944.

Maria Popper died in Vienna on 12 March 1988. In 2007, the Art Restitution Advisory Board recommended the restitution of 21 objects to the legal successors of Michael Ottokar and Maria Popper. The ethnographic artefacts were handed over in 2008.