Rainier Louis Henri Maxence Bertrand de Grimaldi was born in Monaco on 31 May 1923, the only son of the late Comte Pierre de Polignac and Princess Charlotte of Monaco. His education began in England at Summerfields, Hastings, and the Stowe School. From there he continued at Rosey, Switzerland, and the University of Montpelier in France, graduating from the Ecole Libre des Sciences Politiques (Paris) after a noted military career. During World War II, he enlisted in the French army and served with the Seventh Regiment of Tirailleur Algeréins as Lieutenant Grimaldi. In combat during the Alsatian campaign, Prince Rainier was cited for bravery and offered a colonelship, which he declined. The French, Belgian, and Greek governments awarded him medals of honor. He founded the Monaco Red Cross and American Friends of Monaco.
In his youth, the prince devoted his leisure time to tennis and skiing, car racing, and cruises to Africa to obtain live animals for the Monaco National Zoo. From an early age he had no personal interest in gambling, an industry that has symbolized Monaco since its inception in Monte Carlo in 1860. His marriage in 1956 to American movie star Grace Kelly lent a magical aura to his personality and placed him and Monaco in the limelight. Princess Grace's accidental death in 1982 plunged him into mourning for several years, but he is said to have recovered his zest for life and his job. The couple had three children: Caroline, Albert, and Stephanie. Rainier has seven grandchildren.
Some observers mistakenly speculated that he might step down and relinquish the throne to his son Prince Albert on his sixty-fifth birthday in 1988. In 1999, he reiterated his earlier promises to retain the helm until Prince Albert marries. In May 2002, however, giving up hope of his bachelor son ever producing an heir, Rainier changed the rules of succession to allow his daughters, and then their children, to inherit the throne. This move ensured that Monaco would not be unable to produce an heir and thus revert to French ownership as stipulated in the 1918 treaty.