According to the Vadam saga, he lost a war with one of Vadam's rivals. The new Kaidon had Ther and his soldiers placed in the keep's jails, where they were mocked and fed scraps to prolong their miserable lives. Many of his brethren killed themselves in order to keep what was left of their honor. Ther managed to escape after weeks of starvation, becoming thin enough to squeeze through the bars of his window, scale the cliffs below, and enter a valley, before swimming away down river. For many days he walked, eating vermin and whatever else he could find before entering the deserts. There, he wandered for many years, building strength and hardness, making allies from others like him, willing to fight and live no matter the odds.
With his new allies he attacked the keep, scaled the walls of the tower and killed his usurpers. He threw their bodies into the river, which legend had it ran purple with Sangheili blood for a week. Upon reinstatement as Kaidon, he had every inmate of the keep too cowardly to commit suicide executed, and from there rebuilt his family.
His life was added to the "Vadam Saga," a wall with Vadam's history carved into it. 
- Halo: The Cole Protocol (First appearance)