Ferdinand I of Hohenzollern-Sigmaringen (b. 12/24 August 1865, Sigmaringen - d. July 20, 1927, Peles Castle, Sinaia), also called the Integrator, was the second king of Romania, from October 10, 1914 until his death. Ferdinand (born Ferdinand Viktor Albert Meinrad von Hohenzollern-Sigmaringen) was the second son of Prince Leopold of Hohenzollern-Sigmaringen and Princess Antonia of Portugal, daughter of King Ferdinand II of Portugal and Queen Mary II. of Portugal. His family was part of the Catholic branch of the Prussian royal family of Hohenzollern. Ferdinand spent his childhood and adolescence at the family home in Sigmaringen, Germany. In 1885 he graduated from the Kassel Officers' School, and was appointed a second lieutenant in the 1st Guards Regiment at the Royal Prussian Court. He then studied at the University of Leipzig and at the Higher School of Political and Economic Sciences in Tübingen, which he graduated in 1889.

Starting with 1889, he became Crown Prince of the Kingdom of Romania, following the renunciation of his father and older brother, Wilhelm, the rights of succession to the royal crown of Romania. From that moment he settled in Romania, where he continued his military career, having a series of honorary commands, being promoted to the rank of corps general. He married on December 29, 1892, in Sigmaringen, Princess Maria Alexandra Victoria of Saxe-Coburg and Gotha, niece of Queen Victoria, daughter of Duke Albert of Edinburgh and Grand Duchess Maria Alexandrovna Romanov, the only daughter of Tsar Alexander II. of Russia. Ferdinand became King of the Kingdom of Romania on October 10, 1914, under the name of Ferdinand I, following the death of his uncle, King Carol I. He ruled Romania during the First World War, choosing to fight on the side of the Entente against the Central Powers. had the effect of his exclusion from the Royal House of Hohenzollern by Emperor Wilhelm II of Germany. At the end of the war, Romania ended the process of achieving the national-unitary state, by uniting Bessarabia, Bukovina and Transylvania with the Old Kingdom. On October 15, 1922, in Alba Iulia, Ferdinand was crowned King of Greater Romania. In the years following the First World War, Romania underwent a series of profound transformations, especially through the application of agrarian reform and universal suffrage. In 1925, a dynastic crisis broke out, caused by Prince Carol's renunciation of his rights of succession to the Romanian Crown, which led Ferdinand to exclude Carol from the Royal House of Romania and to appoint his son, Mihai, as heir apparent. , who would succeed to the throne. Ferdinand died in Sinaia on July 20, 1927, of galloping colon cancer. He was buried at Curtea de Argeș Monastery.