As he wandered, he picked up on the latest developments in the art, inventing new cocktails and building a serious following for his particular blend of craftsmanship and showmanship, epitomized in his signature drink, the Blue Blazer, a pyrotechnic showpiece in which an arc of flame passed back and forth between two mixing glasses. At the Occidental, Thomas was earning $100 a week, more than the vice president of the United States. When he died, in 1885, newspapers all over the country observed his passing in substantial obituaries.

Thomas’s most celebrated bar was at Broadway and 22nd Street, occupying the basement and one bay of what is now Restoration Hardware. “They really ought to put some sort of plaque there,” Mr. Wondrich said.

On the walls of Thomas’s saloon hung caricatures of the political and theatrical figures of the day, many of them executed by Thomas Nast, including one, now lost, depicting Thomas “in nine tippling postures colossally,” as a newspaper reporter described it. Customers could look at themselves in fun-house mirrors that made them look fat or thin. By this time Thomas was middle-aged, with a wife and two daughters, and at 205 pounds one of the lighter members of the Fat Men’s Association, but still, undeniably, a sport.

Thomas’s life spanned the three great ages of the cocktail, the archaic, the baroque and the classic, a helpful chronology proposed by Mr. Wondrich.

Image Credit... Ross MacDonald

In 1830, the probable year of his birth, the main American mixed drinks were punches, toddies and slings — nothing more than brandy, gin or whiskey sweetened with a little sugar. Thomas found his professional footing in an age of flamboyant creativity, when bartenders experimented with a bewildering array of ingredients and styles, and by the time of his death in 1885 he had seen the birth of the more streamlined modern cocktail typified by the manhattan and the martini.

It is the baroque cocktail that occupied most of Mr. Wondrich’s attention. Thomas, however, could be maddeningly vague in his recipes. Mr. Wondrich was able to determine that a wineglass, as a unit of measure, equaled two ounces. He also discovered that most of the gin recipes envisioned the strongly flavored, malty Dutch gin, not the style known as London dry, which did not take off until the 1890s. Sugar, in Thomas’s age, came in a dense loaf and was less refined than modern white sugar but not as raw as raw sugar (Mr. Wondrich compromises by using Demerara or turbinado sugar, pulverized in a food processor.)