Ferdinand I (12 January 1751 – 4 January 1825), was the King of the Two Sicilies from 1816, after his restoration following victory in the Napoleonic Wars. Before that he had been, since 1759, Ferdinand IV of the Kingdom of Naples and Ferdinand III of the Kingdom of Sicily. He was deposed twice from the throne of Naples: once by the revolutionary Parthenopean Republic for six months in 1799 and again by Napoleon Bonaparte in 1805.

Ferdinand was the third son of King Charles III of Spain, Naples and Sicily by his wife, Maria Amalia of Saxony. On 10 August 1759, Charles succeeded his elder brother, Ferdinand VI, but treaty provisions made Charles ineligible to hold all three crowns. On 6 October, he abdicated his Neapolitan and Sicilian titles in favour of his third son, because his eldest son, Philip had been excluded from succession and his second son, Charles, was heir to the Spanish throne. Ferdinand was the founder of the cadet House of Bourbon-Two Sicilies.

Ferdinand was styled both Ferdinand III of Sicily (6 October 1759 – 12 December 1816) and Ferdinand IV of Naples (6 October 1759 – 23 January 1799; 13 June 1799 – 30 March 1806; 22 May 1815 – 12 December 1816).

On 21 January 1799, the Kingdom of Naples was abolished and replaced by the Parthenopaean Republic which lasted until 13 June 1799. Ferdinand was restored to the throne for a while. On 26 December 1805, Napoleon I of France declared Ferdinand deposed again and replaced him with his own brother Joseph Bonaparte on 30 March 1806.

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