John Gertsen is one of Boston’s most respected and talented bartenders. For six years, he manned the bar at No. 9 Park, developing a reputation not only as a supremely inventive mixologist, but also as an expert on the history of cocktails, particularly drinks from the 19th and early 20th centuries. Gertsen later founded Drink with chef Barbara Lynch in Fort Point. The bar quickly established itself as one of the finest and most original in the city, if not the country.