From Halopedia, the Halo wiki
Kaidons are elected by a panel of their clan's elders. After the kaidon has taken office, any elder who disagrees with the crowning of the new leader sends assassins to kill him or challenges the kaidon himself, as a form of testing whether the new leader is worthy of ruling the clan. Should the assassins fail, the sender is typically executed. However, if the kaidon is killed, no action is taken against the elder, as the Sangheili believe that a kaidon who cannot defend himself is unworthy of leadership. Any treasonous or disloyal individual that lived in the state that the kaidon governed could be executed by the kaidon.
Kaidons, despite being political rulers, are very active in the military, even leading long campaigns into enemy territory, leaving the elders to rule in his stead. Although a kaidon may be protected by numerous armed guards, the kaidon typically removes any threats himself to show that he is a capable leader. A kaidon typically arms himself with an energy sword and may wield a ranged weapon, such as a plasma pistol, as a sidearm. Kaidon is a life-long rank, so the next kaidon is crowned only after the current kaidon dies. In accordance with Sangheili tradition, only males can attain the title of kaidon. As female offsprings of a kaidon are unable to claim their fathers' lands and possessions, other kaidons might contest for a daughter's inheritance by attempting to secure their hand in marriage, either to themselves or to one of their sons. Sangheili history is filled with instances where kaidon daughters rejected suitors and fought them off for years, such as in the case of the Gray Maiden of Konar. Such daughters are given the noble title of Scion.
Kaidons reside within a High Room, located in the kaidon's own keep. The keep that the kaidon lives in is considered the head keep of the state, with there being numerous client keeps controlled by clan elders. A kaidon meets with the elders of the state's client keeps within an assembly house located inside the head keep where matters concerning the state are discussed.
The Refuge was also led by a kaidon. After Kaidon Ussa 'Xellus was forced to leave his state on Sanghelios, he continued to lead the Refuge as its kaidon. After Ussa's death, the Refuge continued to be led by a kaidon by members of the Xellus clan. In the event of a kaidon's absence, another high-ranking Sangheili could be given the "necklace of rank" and serve as the "acting kaidon". During Bal'Tol 'Xellus' term as kaidon, Oska 'Meln challenged his authority and led a rebellion throughout different sections of the Refuge. 'Meln declared himself the kaidon and told his followers that 'Xellus was a "false kaidon".
Eric Nylund's Halo: Ghosts of Onyx makes references to "Major Domo Sangheili". As a "majordomo" is the head (or acting head) of a household, it could be that this was an early concept for the kaidon or elder titles introduced in Halo: The Cole Protocol.
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