The story of the githzerai starts with the beings know as the daelkyr, as in Eberron, all aberrations share a common bond. Thousands of years ago, the daelkyr led an extraplanar incursion into Eberron. True lords of madness, these shapers of flesh brought with them a host of horrors from the plane of Xoriat. As the daelkyr sank their talons into Eberron, they twisted and corrupted any other creatures unfortunate enough to fall into their clutches. Eventually, the shapers of flesh were defeated and sealed in the underworld of Khyber, where they continue to create new terrors even now. Many aberrations — including beholders, mind flayers, and grell — are natives of Xoriat brought to Eberron by the daelkyr. Of these, the mind flayers are the chief servants of the daelkyr.
Eberron is not the first world that the daelkyr attacked. Mind flayers were created when the daelkyr destroyed the native world of the gith races. The githzerai and githyanki are descendants of those few survivors who fled to Kythri in Khyber, and the Sea of Syberis, while the mind flayers are descended from survivors of the gith progenitor race who were twisted in the same manner as the dolgaunts and dolgrims.
When the Gatekeepers severed the connection to Xoriat, the githyanki and githzerai took the opportunity to turn on their mind flayer masters, escaping their slavery en masse. But the two gith races were part of different slave castes and couldn’t get along once they had won their freedom. The githyanki retreated to Syberis, lured by its timeless qualities, while the githzerai went to Kythri to get as far away from the mind flayers as possible. A few githyanki and githzerai stayed on Eberron, and Katal Hazath is one of their communities.
The githyanki and githzerai are bitter rivals who aren’t above raiding each other’s communities, but they are united in their hatred of the mind flayers and anything else that hails from Xoriat. Even rival gith communities sometimes band together to enter Khyber and ensure that the magic seals imprisoning powerful remnants of the Xoriat interlopers remain strong. Other gith communities unite simply to kill as many mind flayers as they can.
Some say Gith was the personal bodyguard of a powerful daelkyr, while others claim she was only a lowly foot soldier and little more than a child. But her mental and physical powers were great, and her rage, hatred, power, and charisma was sufficient to take advantage of the defeat of the daelkyr by the Gatekeepers, and guide the slaves of the illithids to victory. Not every daelkyr or illithid stronghold fell, but the ties that bound them together were broken, and even today the mind flayers have not recovered from their masters’ defeat. Those that did not escape hid themselves away in Khyber, vowing to rebuild their strength and take vengeance against their treacherous former slaves, something they have not managed to do.
Having won the war, Gith continued to treat her people (who would become known as the githyanki, a word meaning “children of Gith”) as a conquering army rather than a free people. Having just won a war, and despite not being trapped in Khyber by the seals of the Gatekeepers as the aberrations were, she prepared to launch a new war, an Eternal Crusade that would exterminate every last illithid once and for all.
While some githyanki were comforted by Gith’s military discipline, others chafed against it. One leader, Zerthimon, was the most vocal of the dissidents. He claimed that Gith would replace the illithid tyranny with her own, and that though she had been successful in the past as a leader of war, she was unfit to lead the People in peace. He called for her to step down. Gith refused, but Zerthimon and his followers would not allow themselves to be ruled by a new tyrant. Having just won a war, now a civil war began among the githyanki, with Zerthimon’s loyalists battling Gith’s.
What happened to Zerthimon is a matter of dispute. Some say Zerthimon was killed, while others say he defeated Gith in single combat, but chose to spare her life. Regardless, the followers of Zerthimon—now known as the githzerai, or “those who spurn Gith”—retreated to Kythri, the Churning Chaos, deep within the Elemental Chaos of Khyber.