After its creation at the dawn of each iteration of reality by the Gamemaster, the title of Barkeep is won by inheritance, election, combat, or subterfuge—or sometimes through a combination of any or all of the above.
The Barkeep runs the day-to-day operations of The Strumpet’s Sister, sometimes isolating themself behind the bar and sometimes wandering amongst the many rooms of the place.
The Barkeep is responsible for serving drinks, of course, and for managing the waitstaff. Beyond that though, they are in charge of the mechanism by which The Strumpet’s Sister changes locations—and they are the sole arbiter on when and where the Sister goes next. This is their most important duty, the charge given to the first Barkeep by the One True Goddess so that she could focus her attentions on the dealings of the House of Thrones upstairs.
During February vacation of the year 1990, a twelve-year-old Robin Gates—stuck in a booth at the bar where her mother had just picked up a part-time job—discovered a newspaper dated sixteen years into the future. She was not supposed to see this. Her discovery was the inciting incident for not only a rather abrupt move of The Strumpet’s Sister, but for Ada Coffin’s eventual ascension to the role of Barkeep.
Some whisper that this was all a part of an extremely long-in-the-making plot by Coffin to escape the Sister, but those whisperings have yet to be proven accurate.
You can to read all about it in the third book in The Stains of Times series, The Chains of Desire.