Robert J. Cooper, founder of St-Germain liqueur — a staple for any self-respecting bartender — died this week at the age of 39.

The native New Yorker passed away Monday in Santa Barbara, Calif. His death was confirmed Thursday by the New York Times, though the cause was not known.

Considered a pioneer in the cocktail world, Cooper was lauded by the liquor industry for years before he sold his uber-popular elderflower liqueur, St-Germain, to Bacardi in 2012 for an undisclosed sum.

“It was more [money] than I expected to see in a lifetime,” Cooper admitted at the time.

The UCLA Santa Barbara grad introduced St-Germain in 2007 to great fanfare. Dubbed the “bartender’s ketchup,” the sweet, floral liqueur distilled from French elderberry blossoms became a must-have for mixologists.

Cooper’s other cocktail creations included Crème Yvette liqueur and Hochstadter’s Slow & Low, a throwback to the Rock & Rye, a 19th-century cocktail of rye sweetened with rock candy.