Let's see here...
Eons ago, a people of incredible piety lived upon the Outlands known as the tiere - a name meaning 'steadfast' in their own tongue - who devoted the tireless work of countless generations toward the construction of a grand temple for their patron god in the hopes that this deity, whose name has been lost to history, would honor their efforts by coming to the temple and dwelling among them, at least for a time.
It was a wonderous marvel of engineering both mundane and magical, vast and beautiful beyond compare, built from every precious material imaginable and many which have since been forgotten, and entire worlds and their stars were born and died in the time needed to finish its construction. And when it was finally complete, the god of the tiere smiled upon his people and took it for his home, as they had wished.
And yet the shadow of this temple stretched far, and other gods took notice and began to covet it - gods more powerful than the one worshiped by the tiere. When word reached the tiere that these interloping powers sought to destroy them and seize the temple by force, they turned to their patron and prayed for him to save them from this coming doom, only to find their entreaties dismissed and refused - their god more concerned with his own safety than that of his ever-faithful people.
Though normally cautious and slow to act, the tiere moved quickly on that day, all who followed their patron god coming together outside the temple built by the toil of untold generations of their people, and as one they began to chant words ancient even in those forgotten times - words to repay an act of infidelity so great that it would condemn a people the like of whose piety has never been seen since. The tiere were destroyed by their revenge, consumed to fuel an arcane ritual of unimaginable power that sealed the temple away, imprisoning and entombing their god within a vault to spend the rest of his immortal, unending days alone. The Temple of the Captive God is lost now, though there are always those fortune seekers who claim to have seen it.
Some time after its disappearance, a people appeared in the wind-torn deserts of Minethys on the plane of Carceri, worshipping no gods and calling themselves the gautiere - a word meaning, in the tongue of the now-vanished tiere, 'once steadfast'. The connection between the two peoples, if any exists, is unknown.
Eberron: King Kaius III is not King Kaius III.
He’s Kaius I, who is a vampire, pretending to be his grandson.
Unless you dig deeper, and maybe he is actually Kaius III in league with his immortal grandfather, spending his days pretending to be his grandfather pretending to be himself. All to keep Kaius’ vampiric sire, and said sire’s master Erandis Vol, from controlling Karrnath.
As an aside, way back in the day when WotC still had its own forums (possibly even pre-Gleemax, but I forget), someone in an Eberron related thread made an "I'm my own Grandpa" comment in reference to the Kaius I/III situation, and my brain, with a brief detour to a relevant episode of Futurama, came up with a plotline where the real Kaius I had died early in life and was secretly replaced by his grandson Kaius III, who had somehow been cast backwards in time, and that this Kaius would continue on as the "Kaius I" known to history and eventually usurp his younger self 100+ years in the future in order to keep the time loop intact.
Also, Kaius I/III can't say anything without sounding like Phillip J. Fry in my head anymore...