Alexandru Ioan Cuza was the first domnitor (ruler) of the Romanian Principalities through his double election as prince of Moldavia on 5 January 1859 and prince of Wallachia on 24 January 1859, which resulted in the unification of the two states. He was a prominent figure of the Revolution of 1848 in Moldavia. Following his double election, he initiated a series of reforms that contributed to the modernization of Romanian society and of state structures.

Principe Domnitor was the official title of the ruler of Romania between 1862 and 1881. It was usually translated as "prince regnant" in other languages and less often as "grand duke". "Domnitor" is an adjective derived from the Romanian word "domn" and, in turn, from the Latin "Dominus". The title Domn had been in use since the Middle Ages and it is also the Romanian equivalent to the Slavic Hospodar. Moldavian and Wallachian rulers had used this term for their title of authority as the head of state, while "voievod" represented the military rank as the head of the army.