Rainier III (Rainier Louis Henri Maxence Bertrand Grimaldi; 31 May 1923 – 6 April 2005) ruled the Principality of Monaco for almost 56 years, making him one of the longest ruling monarchs in European history. Though internationally known for his marriage to the American actress Grace Kelly, he was also responsible for reforms to Monaco's constitution and for expanding the principality's economy beyond its traditional casino gambling base. Gambling accounts for only approximately three percent of the nation's annual revenue today; when Rainier ascended the throne in 1949, it accounted for more than 95 percent.

Rainier was born at Prince's Palace in Monaco, the only son of Prince Pierre of Monaco, Duke of Valentinois and his wife, the Monegasque Hereditary Princess, Charlotte, Duchess of Valentinois. Rainier was the first native-born hereditary prince of Monaco since Honore IV in 1758. Rainier's mother was the only child of Prince Louis II of Monaco and Marie Juliette Louvet; she was later legitimized through formal adoption and subsequently named heir presumptive to the throne of Monaco. Rainier's father was a half-French, half-Mexican who adopted his wife's surname, Grimaldi, upon marriage and was made a prince of Monaco by Prince Louis, his father-in-law. Rainier had one sibling, Princess Antoinette, Baroness of Massy.

Rainier's early education was conducted in England, at the prestigious public schools of Summerfields in St Leonards-on-Sea, Sussex, and later at Stowe, in Buckinghamshire. After England, Rainier attended the Institut Le Rosey in Rolle and Gstaad, Switzerland from 1939, before continuing to the University of Montpellier in France, where he obtained a Bachelor of Arts degree in 1943, and finally to the Institut d'études politiques de Paris in Paris.

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