Ferdinand I (Ferdinand Viktor Albert Meinrad; 24 August 1865 – 20 July 1927), nicknamed Întregitorul ("the Unifier"), was King of Romania from 1914 until 1927. Although a member of Germany's ruling Hohenzollern imperial family, Ferdinand sided against the Central Powers in World War I.

In Sigmaringen on 10 January 1893, Prince Ferdinand of Romania married his distant cousin, the LutheranPrincess Marie of Edinburgh.The marriage produced three sons: Carol, Nicholas and Mircea (one of whom, Mircea, died in infancy) and three daughters: Elisabeta, Maria (Mignon) and Ileana.

October 10, 1914, Ferdinand became King of Romania upon the death of his uncle. Already in the early stages of World War I, Ferdinand maintained Romania’s neutrality until finally entering the war, on the side of the Allied Powers, in August 1916.

Despite the setbacks after the entry into war, when Dobruja and Wallachia were occupied by the Central Powers, Romania fought in 1917 and stopped the German advance into Moldavia. When the Bolsheviks sued for peace in 1918, Romania was surrounded by the Central Powers and forced to conclude the Treaty of Bucharest, 1918. However, Ferdinand refused to sign the treaty.

When the Allied forces advanced on the Thessaloniki front, they knocked Bulgaria out of the war, and Ferdinand ordered the re-mobilization of the Romanian Army. Romania re-entered the war on the side of the Triple Entente.

During the war, Ferdinand and his wife traveled extensively to support the troops and boost morale amongst the Romanian people. By the end of the war, through Ferdinand’s leadership, the Kingdom of Romania had grown to include the regions of Bessarabia, Bukovina, and Transylvania.