Who is Bryan that the Stage Manager referred to in Act !? Fictitious or a reference to someone?

It is a reference to a historical figure. The Stage Manager tells us the day is May 7, 1901, but that doesn't matter much -national events are hardly mentioned (aside from the paperboy's coming death in World War I), technological advances have no bearing on the characters, and the only connection to real historical figures is an aside that "[William Jennings] Bryan once spoke there." Bryan was an American orator and politician from Nebraska.