Theodore I of Corsica (25 August 1694 – 11 December 1756), born Theodor Stephan Freiherr von Neuhoff, was a German adventurer who was briefly King of Corsica. Theodore is the subject of an opera by G. Paisiello, Il Re Teodoro in Venezia (1784, Vienna), and one of the six kings in Venice in Voltaire's Candide.
Theodor von Neuhoff was born in Cologne as the son of a Westphalian nobleman. Educated at the court of France, he served first in the French army and then in that of Sweden. Baron de Goertz, minister to Charles XII, realizing Neuhoff's capacity for intrigue, sent him to England, and to Spain to negotiate with Cardinal Alberoni. Having failed in this mission he returned to Sweden and then went to Spain, where he served Alberoni until his exile, then the Baron Ripperda, and was made colonel and married one of the queen's ladies-in-waiting. Deserting his wife soon afterwards he repaired to France and became mixed up in John Law's financial affairs and the Mississippi Company boom; then he led a wandering existence visiting Portugal, the Netherlands, and Italy.
At Genoa, Neuhoff made the acquaintance of some Corsican rebels and exiles, and persuaded them that he could free their country from Genoese tyranny if they made him king of the island. With the help of the Bey of Tunis, he landed in Corsica in March 1736 with military aid. The islanders, whose campaign had not been successful, elected and crowned him king. He assumed the title of King Theodore I, issued edicts, instituted an order of knighthood, and waged war on the Genoese, at first with some success. But in-fighting among the rebels soon led to their defeat. The Genoese put a price on his head and published an account of his colourful past, and he left Corsica in November 1736, ostensibly to seek foreign assistance. After sounding out the possibility of protection from Spain and Naples, he set off to Holland where he was arrested for debt in Amsterdam.