After World War I, the casino in Monte Carlo was in trouble. The world had changed, particularly the world of money, and the Prince of Monaco, Louis II, believed the casino's aged owner, Camille Blanc, had lost touch. As the casino supplied the principality with revenue, he sought to replace Blanc and bring in fresh business management. For assistance, he approached Sir Basil Zaharoff, an international financier and arms dealer who had long been a patron of the Côte d’Azur. Zaharoff managed to get hold of the shares and, with the aid of the Prince, shouldered Blanc out and became the casino's master. Zaharoff brought in fresh administration and the result paid huge dividends.
In 1953, Greek shipping magnate Aristotle Onassis bought up the shares of SBM via the use of front companies in the tax haven of Panama and took control of the organisation, moving his headquarters into the Old Sporting Club on Monaco's Avenue d'Ostende shortly after. Onassis's takeover of the SBM was initially welcomed by Monaco's ruler, Prince Rainier III, as the country required investment, but Onassis and Rainier's relationship had deteriorated by 1962 in the wake of the boycott of Monaco by the French president, Charles de Gaulle. Onassis and Rainier had differing visions for Monaco. Onassis wished the country to remain a resort for an exclusive clientele, but Rainier wished to build hotels and attract a greater number of tourists. Monaco had become less attractive as a tax haven in the wake of France's actions, and Rainier urged Onassis to invest in the construction of hotels. Onassis was reluctant to invest in hotels without a guarantee from Rainier that no other competing hotel development would be permitted, but promised to build two hotels and an apartment block. Unwilling to give Onassis his guarantee, Rainier used his veto to cancel the entire hotel project, and publicly attacked SBM for their ‘bad faith’ on television, implicitly criticising Onassis. Rainier and Onassis remained at odds over the direction of the company for several years, and, in June 1966, Rainier approved a plan to create 600,000 new shares in SBM to be permanently held by the state, which reduced Onassis's stake from 52% to under a third. In the Supreme Court of Monaco, the share creation was challenged by Onassis who claimed that it was unconstitutional, but the court found against him in March 1967. Following the ruling, Onassis sold his holdings in SBM to the state of Monaco for US$9.5 million, and left the country.
