Ferdinand is a name used by kings and princes of several countries.

Aragon

Ferdinand I of Aragon - the Just; 1379-1416; became king 1412.
Ferdinand II of Aragon - a.k.a. Ferdinand V of Spain

Austria
Ferdinand I of Austria - 1793-1875; became emperor 1835.
Ferdinand III, Archduke of Austria - see Ferdinand III, grand duke of Tuscany.
Ferdinand IV, Archduke of Austria, duke of Modena.

Bulgaria
Ferdinand of Bulgaria

Germany
Ferdinand I, Holy Roman Emperor - 1503-1564; became emperor 1556.
Ferdinand II, Holy Roman Emperor - 1578-1637; became emperor 1619.
Ferdinand III, Holy Roman Emperor - 1608-1657; became emperor 1637.

Naples
Ferdinand I of Naples - ca.1424-1494; became king 1458.
Ferdinand II of Naples - 1469-1496; became king 1495.
Ferdinand III of Naples - see Ferdinand II of Aragon.
Ferdinand IV of Naples - 1751-1825; first became king 1759.

Two Sicilies
Ferdinand I of the Two Sicilies - see Ferdinand IV of Naples
Ferdinand II of the Two Sicilies - 1810-1859; became king 1830.

Portugal
Ferdinand of Portugal - 1816-1885; became titular king 1837.

Spain
Ferdinand I of Castile and Leon - the Great; ca.1000-1065, became king 1037.
Ferdinand II of Leon - d. 1188.
Ferdinand III of Castile and Leon - the Saint; ca.1200-1252; became king of Castile 1217, of Leon 1230.
Ferdinand IV of Castile and Leon - 1285-1312; became king 1295.
Ferdinand V of Spain - the Catholic; 1453-1516; became king -
Ferdinand VI of Spain - 1712-1759; became king 1746
Ferdinand VII of Spain - 1784-1833; became king 1808
Ferdinand of Austria, Cardinal-Infante of Spain - 1618-1641

Tuscany
Ferdinand III, Grand Duke of Tuscany - 1769-1824; became grand duke 1790.
Ferdinand IV, Grand Duke of Tuscany - b.1835; grand duke 1859-1860.

Brunswick-Lüneburg
Ferdinand, Duke of Brunswick - 1721-1792.

Bulgaria
Ferdinand Maximilian, prince of Bulgaria - b.1861; became ruler 1887.

Romania
Ferdinand of Romania - b.1865; became presumptive heir 1888.