Ladislaus (from 1906, Freiherr) Hengelmüller von Hengervár (Hungarian: hengervári báró Hengelmüller László) (2 May 1845 – 22 April 1917), was an Austro-Hungarian diplomat of Hungarian origin who was a long-term Ambassador at Washington D.C., throughout many Presidential administrations including those of William McKinley, Theodore Roosevelt and William Taft.