Harry MacElhone of Harry's Bar in Paris, was the creator of (among others) the *Bloody Mary in 1921 and the Sidecar in 1931.
The Blue Lagoon was invented by his son Andy, in 1972.
* Many sources credit Harry MacElhone himself with the creation of the Bloody Mary. The following information is more likely correct:
"The Bloody Mary was created by Fernand "Pete" Petiot, a bartender at Harry's NY Bar Paris, and he was brought to NYC shortly after repeal of prohibition to work at the King Cole Bar in the St Regis Hotel. The name of the drink was changed to the Red Snapper for a while, but eventually it was again known as the Bloody Mary.”
(source: Gary Regan, Ardent Spirits