Oskar Reinhart (1885–1965), born into an old family of Winterthur merchants, was one of the most important art collectors and patrons in Switzerland. His mother, Lilly Reinhart-Volkart (1855–1916), was heir to his grandfather's company – Volkart Brothers, which was founded in 1851. His father Theodor Reinhart (1849–1919) expanded the company and successfully pioneered trade between India and continental Europe.
As early as 1907, when still a trainee in his parents’ company, Oskar Reinhart began to collect old master and modern prints. He did not, however, acquire the bulk of his art collection until after his father's death. Until 1924, Oskar Reinhart remained an active – and until 1939 a silent – partner of the Volkart trading company. Thus, he devoted himself entirely to expanding his art collection. In addition, he served in various public bodies such as the Swiss Gottfried Keller-Foundation, whilst his brother George (1877–1955) and Werner (1884-1951) controlled the company until 1952. In 1924, Oskar Reinhart purchased a mansion at “Am Römerholz”, which he converted into his private residence and which he furnished with exquisite works of art.
In 1936, Reinhart helped the Munich-based art dealer Fritz Nathan to immigrate into Switzerland. In 1941, he also attempted – together with Fritz Nathan and Walter Feilchenfeldt – to enable Max Liebermann's widow to emigrate to Switzerland. Furthermore he was mindful not to purchase any artwork from dubious sources during the Third Reich. He did, however, under the impression of the events of time, create the Oskar Reinhart Foundation on 10 October 1940, and donated his works by German, Austrian and Swiss artists from the 18th to early 20th century to this foundation. Due to the War, the old school building adjacent to the Stadtgarten [City Park] that had been remodelled as a museum for the foundation was not opened until 1951. Reinhart left the collection of paintings and drawings by German, Dutch, English, Italian, Spanish and French Old Masters as well as Impressionists that he had kept in his private house “am Römerholz” to the Swiss Government, while his print collection was given to the “Oskar Reinhart Foundation”.