Charles III (Spanish: Carlos III; Italian: Carlo III; 20 January 1716 – 14 December 1788) was the King of Spain and the Spanish Indies from 1759 to 1788. He was the eldest son of Philip V of Spain and his second wife, the Princess Elisabeth Farnese. In 1731, the fifteen-year-old Charles became the Duke of Parma and Piacenza, as Charles I, at the death of his childless great uncle Antonio Farnese, Duke of Parma.

In 1734, as the Duke of Parma, he conquered the kingdoms of Naples and of Sicily, and was crowned as the King of Naples and Sicily on 3 July 1735, reigning as Charles VII of Naples and Charles V of Sicily. In 1738 he married the Princess Maria Amalia of Saxony, an educated, cultured woman who gave birth to thirteen children, eight of whom reached adulthood. Charles and Maria Amalia resided in Naples for nineteen years; she died in 1760.

Upon succeeding to the Spanish throne on 10 August 1759, Charles, a proponent of enlightened absolutism, on 6 October 1759 abdicated the Neapolitan and Sicilian thrones in favour of Ferdinand, his third surviving son, who became Ferdinand I of the Two Sicilies, or Ferdinand IV of Naples and III of Sicily. Charles III's descendants ruled the Kingdom of the Two Sicilies until 1861.

Carlos III may refer to:

John Adams (October 30, 1735 (O.S. October 19, 1735)  – July 4, 1826) was an American Founding Father, and the second President of the United States (1797–1801). He was also a lawyer, statesman, diplomat, political theorist, and a leading champion of independence in 1776. Hailing from New England, Adams, a prominent lawyer and public figure in Boston, was highly educated and represented Enlightenment values promoting republicanism. A Federalist, he was highly influential and one of the key Founding Fathers of the United States.

Adams came to prominence in the early stages of the American Revolution. As a delegate from Massachusetts to the Continental Congress, he played a leading role in persuading Congress to declare independence and assisted Thomas Jefferson in drafting the Declaration of Independence. As a diplomat in Europe, he was a major negotiator of the eventual peace treaty with Great Britain, and chiefly responsible for obtaining important loans from Amsterdam bankers. A political theorist and historian, Adams largely wrote the Massachusetts Constitution in 1780 which soon after ended slavery in Massachusetts, but was in Europe when the federal Constitution was drafted on similar principles later in the decade. One of his greatest roles was as a judge of character: in 1775, he nominated George Washington to be commander-in-chief, and 25 years later nominated John Marshall to be Chief Justice of the United States.