Ferdinand IV of Naples, later known as Ferdinand I of the Two Sicilies, was born on January 12, 1751, in Naples, and died on January 4, 1825, in the same city. He was the son of Charles III of Spain and Maria Amalia of Saxony. When his father acceded to the Spanish throne in 1759, Ferdinand inherited the Italian kingdoms of Naples and Sicily, due to international treaties that prevented the union of the crowns of Spain and Italy in a single person.

He simultaneously held the titles of:

• Ferdinand IV of Naples (reigned three times: 1759-1799, 1799-1806 and 1815-1816)

• Ferdinand III of Sicily (1759-1816)

In 1816, with the formal union of both kingdoms, he became the first King of the Two Sicilies, ruling this new kingdom until his death in 1825.

During his reign, he faced crucial events such as the Napoleonic invasions. He was deposed in Naples in 1799 when the short-lived Neapolitan Republic was established, and again in 1806 by Napoleon, who appointed his brother Joseph Bonaparte as king. Ferdinand took refuge in Sicily and was restored to Naples after Napoleon's fall in 1815, crowning himself King of the Two Sicilies the following year.

His government was initially supported by ministers such as Bernardo Tanucci and later by figures such as John Francis Edward Acton. He actively participated in coalitions against France during the French Revolution and the Napoleonic Wars. He governed with an autocratic policy and faced pressure for reforms and autonomy, especially in Sicily, where he was forced to concede the Constitution of 1812.

He married first Maria Carolina of Austria, with whom he had several children, and then Lucia Migliaccio of Florida.

Ferdinand I is remembered both for his long stay on the Neapolitan throne and for consolidating the Kingdom of the Two Sicilies, uniting Sicily and Naples under a single kingdom.