Freiherr Ladislaus 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.

[3] In 1887, Hengelmüller was appointed to serve as minister at Belgrade in the wake of the Serbo-Bulgarian War of 1885-1886 and had to exercise a restraining influence on Serbian King Milan I, whose throne depended on Austro-Hungarian support.

Described as clever and experienced, Hengelmüller von Hengervár became greatly popular and well-respected during his long period of service in Washington D.C.[5] In late 1902, he was informed that his legation would be upgraded to an embassy and that he would be promoted to the rank of ambassador.

[10] Baron Hengelmüller von Hengervár was present on 10 January 1908 at the Waldorf Astoria in New York City when the American Priory of the Sovereign Order of Saint John of Jerusalem was officially incorporated.

[18] He was succeeded as US Ambassador by Konstantin Dumba, who held the post until 1915 when he was declared persona non grata and expelled from the country by President Wilson.

[19] Together, they were the parents of: Baron Hengelmüller von Hengelvár died on 22 April 1917 at Abbazia (now Opatija), one of the leading health resorts of the Habsburg Empire located in Istria.