Banker. Founder of Mendelssohn & Co., one of Europe's preeminent financial institutions for over a century. Mendelssohn was born in Berlin, Germany, the son of German-Jewish philosopher Moses Mendelssohn. Unlike four of his five siblings, who converted to Christianity, Joseph remained faithful to Judaism his whole life. With aid from wealthy family connections he started a Berlin banking house as Mendelssohn and Friedlaender in 1795. His brother Abraham became a partner in 1804 and the firm was renamed J & A Mendelssohn, with new headquarters in Hamburg. This city was invaded by the French Army in 1810; the brothers were less than cooperative with the occupying forces and the following year they had to flee in disguise to Berlin. They were heavily fined for refusing to help fund Napoleon's 1812 Russian campaign (which would have been a bad investment, as it turned out). After Napoleon's defeat in 1815, the Mendelssohns established themselves in the heart of Berlin's financial district and joined a consortium of German banks, led by the House of Rothschild, to secure war reparations from France. Joseph opened a Paris branch for this purpose. In 1822 Abraham sold his partnership and in 1827 Joseph reorganized the business as Mendelssohn & Co., which he ran successfully until his death. Under the leadership of his son Alexander Mendelssohn, Mendelssohn & Co. became Germany's most important private bank through investments in government projects and railroad construction. They served as the Royal Bankers to the Russian Czars from the 1850s to the start of World War I. It was owned and operated by the Mendelssohn family until shortly before its liquidation by the Nazis in 1938. There is a commemorative plaque on its former office building in Berlin. Joseph was the uncle of composers Felix Mendelssohn and Fanny Mendelssohn.