Qui Sait? by Lancome: launched in 1937. Created by Armand Petitjean.
Peut-Être ("Perhaps" in French) became Qui Sait ("Who Knows" in French) in 1956, however I have found publications dating to as early as 1946 using the name Qui Sait (US Patent Office info). The reason for the name change is that it would be easier for Americans to pronounce.
The name Qui Sait was used previously by another French perfumer, Lournay in 1925.