Kaidon

Kaidon, or "clan leader", is a meritocratic rank held by the head of a Sangheili state. Kaidons are chosen by elders of their state.

Overview
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, 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.

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. Kaidon is a life-long rank, so the next kaidon is crowned only after the current kaidon dies.

Known kaidons

 * Ther 'Vadam - An ancient kaidon of the state of Vadam. After losing a war against one of his clan's rivals, he was imprisoned, though he eventually escaped. He spent years gathering allies, with whom he one day attacked his enemies' keep. He executed his enemies, as well as his former companions who were too cowardly to commit suicide.
 * Unidentified kaidon of Decided Heart - This kaidon was the target of a coup attempt by Ripa 'Moramee, one of his clanmates. 'Moramee's attempt failed and he was brought before the kaidon, who banished him to the Weeping Shadows of Sorrow penitentiary. 'Moramee's resolve during the coup led to his ascencion to the rank of Arbiter.
 * Thel 'Vadam - The latest known kaidon of Vadam; killed the assassins sent by the elder Koida 'Vadam, then executed the latter and banished his family. Later he became the Supreme Commander of the Fleet of Particular Justice, and the Arbiter after that. After becoming the Arbiter, he killed the Prophet of Truth, effectively ending the Human-Covenant War. After the Great Schism, he sought reconciliation with humanity following the war, drawing ire from more conservative Sangheili.
 * Levu 'Mdama - Kaidon of the State of Mdama following the Human-Covenant War in 2553. Allied himself with Thel 'Vadam and sought reconciliation with humanity.

Trivia
Eric Nylund's Halo: Ghosts of Onyx makes reference 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 of the kaidon title used in Halo: The Cole Protocol.

List of appearances

 * Halo: The Cole Protocol
 * Halo: Glasslands
 * Halo Wars: Genesis