Arnold Friedrich Georg Diestel (2 March 1857 – 3 January 1924) was a German politician and a First Mayor of Hamburg. Diestel was born in Valparaíso, Chile and died in Hamburg. In 1908 the Hamburg Parliament elected Diestel lifelong senator of Hamburg, replacing the late Johann Georg Mönckeberg. On 12 November 1918 the Hamburg revolutionary Soldiers' and Workers' Council deposed the Senate of Hamburg, but reappointed the senators as acting administration only on November 18. In this function Diestel continued during the Weimar Republic, until the complete senate resigned on 27 March 1919, thus ending the life-term mandates under Hamburg's old 1860 constitution.