Ferdinand I (Ferdinand Viktor Albert Meinrad; 24 August 1865 – 20 July 1927), nicknamed Întregitorul ("the Unifier"), was King of Romania from 10 October 1914 until his death in 1927.

Born in Sigmaringen in southwestern Germany, the Roman Catholic Prince Ferdinand Viktor Albert Meinrad of Hohenzollern-Sigmaringen. The name was later shortened simply to Hohenzollern after the extinction of the Hohenzollern-Hechingen branch in 1869. The princes of Hohenzollern-Sigmaringen had ruled the principality until 1850, when it was annexed to Prussia.

Ferdinand I was the son of Leopold, Prince of Hohenzollern-Sigmaringen, and Infanta Antónia of Portugal (1845–1913), daughter of Queen Maria II of Portugal and Prince Ferdinand of Saxe-Coburg and Gotha, heir to the Slovakian-originated Hungarian magnates of Kohary on his mother's side.

Following the renunciations, first of his father in 1880 and then of his elder brother Prince Wilhelm of Hohenzollern-Sigmaringen in 1886, young Ferdinand became the heir-presumptive to the throne of his childless uncle, King Carol I of Romania, who would reign until his death in October 1914. In 1889, the Romanian parliament recognized Ferdinand as a prince of Romania. The Romanian government did not require his conversion to Eastern Orthodoxy from Catholicism, as was the common practice prior to this date, thus allowing him to continue with his born creed, but it was required that his children be raised Orthodox, the state religion of Romania. For agreeing to this, Ferdinand was excommunicated from the Catholic Church, although this was later lifted.

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