[4] After the First World War Wassermann accepted an invitation to become a member of the German Standing Finance Commission, established under the leadership of Max Warburg.

Meanwhile, in 1922, at the request of Chancellor Cuno he prepared a report and plan to deal with the crisis created by the unaffordability of the reparations requirements imposed on Germany at Versailles in 1919.

The term is sometimes translated in English language sources as "CEO", which can be misleading: he was a leading member of the board, but there would have been no question of implementing significant strategic changes without the support of senior colleagues, some of whom made no secret of their objections to his (it was said) autocratic manner, and were also known to give vent to concerns over the extent to which Wassermann's spare time and (by this time very considerable) personal wealth were used on behalf of Jewish organisations.

Agreement was announced, to widespread astonishment within and beyond the banking establishment, in September 1929 and the merger took effect on Tuesday 29 October 1929, long before the Great Depression's nature and extent of the backwash in Germany (and elsewhere) from the Wall Street crash could be foreseen.

Disconto-Gesellschaft came to the union exceptionally well capitalised, and with a long-established well diversified portfolio of profitable investments in Germany's industrial giants and more widely across Europe.

Deutsche Bank had been established more recently and had grown more rapidly, although it was also well integrated in the German industrial economy and well capitalised by the criteria of the time.

[9] Oscar Wassermann married firstly Hungarian-born Margarethe "Grete" Fürst (1892–1924) and secondly Katharina "Käthe" Haupt (1882–1942), the widow of Prof. Dr. Albert Niemann (1880–1921).

Members of the Jewish banking elite would, in most cases, not have identified or associated much with Jews from the working classes, many of whose families had arrived in Germany only one or two generations earlier, driven to move west by the Russian pogroms and equivalent intensifying pressures elsewhere in eastern-central Europe.

[13] In 1898 he became a member of Gesellschaft der Freunde [de], a genteel and long established Berlin-based Jewish welfare support organisation of which, from 1924 to 1934, he would serve as president.

[14] He became chairman of the German offshoot of "jüdische Palästinawerkes" ("Keren Hayesod") and of the associated funding operation, "Palästina Grundfonds (KH) e. V", established in 1922 with the primary objective of acquiring land in Palestine.

[2][15][16] Wassermann served as deputy chairman of the "Verein zur Gründung und Erhaltung einer Akademie für die Wissenschaft des Judentums", founded in 1919 to create and maintain an academy of Judaic Sciences and Humanities: he organised fundraising on the association's behalf.

He was identified, unfairly, as one of those responsible for the so-called "Versailles Treaty of Shame", and defamed as a "representative of Jewish high finance".

However, shortly before the annual general meeting of 1933, over which Wassermann was scheduled to preside in his capacity as "Sprecher", colleagues announced his retirement "on grounds of age".

One of the works in question, auctioned to "an unknown buyer" courtesy of Paul Graupe in June 1936, is "der Heiratskontrakt" ("The marriage contract" / "O Casamento Desigual") attributed to the Flemish master, Quentin Matsys, which is currently believed to be in Brazil.

The painting hit the headlines there in 2013, with a dispute as to its ownership between the São Paulo Museum of Art, which had accepted it in good faith as a donation, and surviving heirs of Oscar Wassermann, forced to sell it in 1936 in order to escape what turned out to be the looming Holocaust.