From Wikipedia, the free encyclopedia Rainier III (Rainier Louis Henri Maxence Bertrand Grimaldi; 31 May 1923 – 6 April 2005) was the Prince of Monaco from 1949 to his death in 2005. 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 from its traditional casino gambling base to its current tax haven role.