After four years with Königswärter, Wertheim returned to Wertheim & Gompertz and was appointed chief clerk. In 1858 he married his cousin, the only daughter of his uncle, and was thereupon appointed partner of the bank. Until his death in 1897, he was the key partner of the firm. He had succeeded in transforming this modest securities house into a leading player in the national and international underwriting business, in particular American and Russian railroads. Wertheim was considered as the most influential and creative Jewish banker of his time in the financial world of the Netherlands. In fact he belonged to the select circle of men such as Marten Mees17 and S.P. van Eeghen of Van Eeghen & Co., who by their personal and financial engagement, supported the creation, the financing and even restructuring of important Dutch enterprises. During the sugar crisis of 1884 he managed to find the funds to rescue the most important colonial bank, the Nederlandsch-Indische Handelsbank18, which was on the brink of bankruptcy. He was also successfully involved with the organisation and financing of the Dutch and the colonial railway systems and the reorganization of the Vereeniging voor den Effectenhandel19 in 1876. During his career, he was instrumental in the start up of several new banks, such as the Amsterdamsche Bank20 and the NCDB. Because of his reputation, he was also invited on several supervisory boards, among them the central bank De Nederlandsche Bank and the Amsterdamsche Bank.

Louis-Raphaël Bischoffsheim (1800-1873), who came from Mainz in Germany, started a bank under his own name L.R. Bischoffsheim in Amsterdam in 1820. According to his nephew, Louis Bamberger, this was the Stammhaus . A few years later after an apprenticeship in Amsterdam, his younger brother Jonathan-Raphaël Bischoffsheim (1808-1883) established himself in the port city of Antwerp. The two brothers married two sisters, who were the daughters of the banker Hayum Salomon Goldschmidt from Frankfurt. This family connection would lead to the creation of a group of associated banks. In 1846 Louis-Raphaël Bischoffsheim moved to Paris to start a new banking house under the name of Bischoffsheim, Goldschmidt & Cie. In London the firm Bischoffsheim, Goldschmidt & Avigdor was founded. This was followed by Bischoffsheim, Cassel & De Hirsch in Brussels in 1857. The old Amsterdam firm was in liquidation in 1862.

17. Managing partner of R. Mees & Zoonen (1720), which became Bank Mees & Hope, MeesPierson, Fortis Bank Nederland and finally ABN AMRO Bank as the result of the mergers in the Dutch banking sector over the years.

18. Netherlands Indies Commercial Bank

19. Association of Securities Dealers that have a seat on the Amsterdam Stock Exchange, today part of Euronext.

20. Became Amsterdam-Rotterdam Bank and then ABN AMRO Bank as a result of the concentration of banks in the Netherlands.

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