Charles (Carlos) II of Spain (November 6, 1661 - November 1, 1700) was king of Spain, Naples, and Sicily, reigning 1665 - 1700. He was the son of his predecessor, King Philip IV of Spain (a Habsburg) and his second Queen, Mariana of Austria, another Habsburg.

He was the last of the Spanish Habsburg dynasty, physically disabled and mentally retarded and disfigured (partly through possession of mandibular prognathism). He may also have suffered from the bone disease acromegaly. Carlos was sadly weak in mind and body, barely able to walk and speak. His pitiful condition was due to the chronic inbreeding within the House of Habsburg.

His mother was his regent during much of his reign. Though she was exiled by the king's illegitimate brother John of Austria the Younger (not the similarly named Don John of Austria), she returned to the regency after John's death.

During his reign, Spain continued its decline that had begun under his increasingly incompetent Habsburg ancestors. However, a peace treaty with Portugal in 1668 ceded the enclave of Ceuta, in North Africa, to Spain.

In 1679, Carlos II married Marie Louise (1662 - 1689), daughter of Philippe I of Orléans, the only brother of Louis XIV. He proved impotent and no children were born. Marie Louise became deeply depressed and morbidly obese, and died in 1689, leaving a distraught Carlos. He had a second marriage to Maria Anna of Bavaria, a princess of Neuberg and sister-in-law of Leopold I, Holy Roman Emperor. However, this marriage was no more successful than the first. Towards the end of his life Carlos became increasingly hypersensitive and strange, at one point demanding that the bodies of his family be exhumed so he could look upon the corpses. He reportedly wept upon viewing the body of his wife, Marie Louise.

By the last two years of his life, he was virtually helpless: he was completely lame, bald, deaf, nearly toothless, and almost blind; he was also prone to epileptic fits.

Carlos II named Philippe de Bourbon, Duke of Anjou as his successor, which provoked the War of the Spanish Succession upon his death in 1700.