Who won the Palme d'Or at the Cannes Film Festival and which winner did I already see...?
Starting 1946 with the first official edition of the Cannes International Film Festival, when several prizes were awarded. From 1946 to 1954 was called Grand Prix and especially in the first two editions, there were several movies who won the Grand Prix.
The first winner of the Palme d'Or was "Marty" in 1955. From 1964 to 1974, the Festival resumed a Grand Prix. Since 1975 the Palme d'Or is the main prize.
Excluded are 1948 and 1950, as no festival could be held because due to budgetary problems. 2020 is excluded as due to the Covid-19 pandemic, no festival was held.
All these informations can be found on the official website of the Festival de Cannes.