Overview
The Master leads the Star Fall Society and is Cheng's primary mentor on his path to becoming the God Slayer. Pathea describes him as wise and enigmatic, the figure who gathers scattered resistance fighters into a force capable of challenging the gods. He is himself an Elemancer, schooled in the Qi arts the Celestials tried to stamp out. Pathea has not said whether he lived through The God Fall himself, nor detailed what he teaches Cheng or how that training is structured.
Background
Pathea has not published a backstory for the Master. What the game's own description establishes is narrow: he leads the Star Fall Society, the Society is supported by a cadre of skilled Elemancers, and Elemancers were hunted down in the purge that followed the God Fall. Whether he was among those who lived through that night, and what he did before it, are not addressed anywhere that has been made public.
Role in the Star Fall Society
The Society's stated objective is to overthrow the Celestials and reclaim the fate of humanity, and it works by drawing scattered resistance fighters together rather than by open confrontation. Pathea describes Cheng as a willing ally who joins that cause rather than a recruit the Master commands. How the Master sets the Society's priorities, and how much of its strategy the player influences, has not been described.