Monaco / Prince Rainier III

Rainier III (born Rainier Louis Henri Maxence Bertrand Grimaldi) 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 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.