The Prince-Bishop of Rome-Ruthenia is the senior-most office and title of the Pontifical Imperial State of Rome-Ruthenia and the United Roman-Ruthenian Church. It is held by the Roman-Ruthenian Pope as Supreme Pontiff of the Church. His office is semi-hereditary, semi-elective, in accordance with the laws of the United Roman-Ruthenian Church. The most formal style of the Pope is His Apostolic Highness the Most Holy. That may be shortened to His Apostolic Highness, but never merely to Highness. The shortened form is, rather, His Holiness. He is principally known as the Roman-Ruthenian Pope.

His other titles include:

Pope-Catholicos of Rome-Ruthenia (Patriarchal title)
Supreme Pontiff of the United Roman-Ruthenian Church
Legate of Christ and Servant of the Servants of Christ
Florentine Archfather
Caesar Augustus, Prince of the Romans, Emperor, and Archprince of Rome-Ruthenia
Grand Duke and titular King of Ruthenia and titular Tsar of All Rus' (Old Russian State)
Archbishop and Metropolitan of Aquileia, Titular Archbishop and Metropolitan of Leontopoli, Titular Bishop of Iconium
Duke and Cardinal Prince of Florence, Imperial Lord of Italy, Naples, Walsingham, and the Floridas
Prince Archbishop and Elector of Würzburg, Prince and titular King of Etruria in the Holy Roman Empire
Duke of Franconia and Archduke of Zagros
Grand Prince of Kiev, Prince of Galicia-Volhynia, Vladimir, Novgorod, Peremyshl, Belz, Zvenygorod, and Terebovlia
Prince, Duke, and Marquis of Santa Croce, Prince, Duke, Marquis, and Count of Monte Titano, Prince McIan of McShane
Count of Sainte Animie, Valais, Daniell, Santa Croce, Vanzy, Johnson, Sommerhausen, Hausen bei Würzburg, Theilheim, and Estenfeld
Baron of Saint Martin and Johnson, Lord des Loges, and others.

Further information

Roman-Ruthenian Pope · Apostolic Highness