During his reign, he was responsible for the transformation of Monaco's economy, shifting from its traditional casino gambling base to its current status as a tax haven and cultural destination.

Rainier died in April 2005 from complications relating to a lung infection as a result of frequent smoking; he was succeeded by his son, Albert II.

Rainier's father, Count Pierre of Polignac, who was half-French and half-Mexican, adopted his wife's dynasty, Grimaldi, upon marriage and was made a Prince of Monaco by his father-in-law.

Rainier received the French Croix de Guerre with bronze star (representing a brigade level citation) and was given the rank of Legion of Honor in 1947.

[2] After ascending the throne, Rainier III worked to recoup Monaco's lustre, which had become tarnished through financial neglect and scandal (his mother, Princess Charlotte, took a noted jewel thief known as René the Cane as her lover).

Monaco's traditional gambling clientele, largely European aristocrats, found themselves with reduced funds after World War II.

To compensate for the loss of income, Rainier decided to promote Monaco as a tax haven, commercial centre, real-estate development opportunity, and international tourist attraction.

[4] The early years of his reign saw the overweening involvement of the Greek shipping tycoon Aristotle Onassis, who took control of the Société des Bains de Mer and envisioned Monaco as solely a gambling resort.

[6] At the time of his death, he was the world's second longest-serving living head of state, just below the King of Thailand, Bhumibol Adulyadej, and the longest-reigning monarch in Europe.

[7][8] In the 1940s and 1950s, Rainier had a ten-year relationship with the French film actress Gisèle Pascal, whom he had met while a student at Montpellier University,[3] and the couple lived at Saint-Jean-Cap-Ferrat.

[citation needed] Rainier's sister, Princess Antoinette, wishing her own son to ascend the throne, spread rumors that Pascal was infertile.

[12] The Prince met Academy Award–winning actress Grace Kelly in 1955, during a photocall at the Palace scheduled to support her trip to the Cannes Film Festival.

In 1979, the Prince made his acting debut alongside the Princess in a half-hour independent film, Rearranged, produced in Monaco.

After its premiere in Monaco, Princess Grace showed it to ABC TV executives in New York in 1982, who expressed interest if extra scenes were shot.

However, Grace died in a car crash caused by a cerebral hemorrhage in 1982, making it impossible to expand the film for an American release.