The Legion of Honor was the gift of Alma de Bretteville Spreckels, wife of sugar magnate Adolph B. Spreckels.

The building is a full-scale replica, by George Applegarth and H. Guillaume, of the French Pavilion at the 1915 Panama Pacific International Exposition, which in turn was a three-quarter-scale version of the Palais de la Légion d'Honneur in Paris

At the close of the exposition, which was located just a few miles away, the French government granted Spreckels permission to construct a permanent replica of the French Pavilion, but World War I delayed the groundbreaking until 1921.

Source: Wikipedia