Kaidon
From Halopedia, the Halo wiki
The Kaidon is a Sangheili theocratic rank. The head of a Sangheili State is referred to as the "Kaidon". Kaidons are elected by Elders of their State.[1]
After election, it is considered a tradition that any elder who disagrees with the election of the new Kaidon send an assassin to kill him, as a form of testing whether the Kaidon is worthy of ruling. Should the assassins fail, the sender is most likely executed, as was Koida 'Vadam, the elder that attempted to have Thel 'Vadamee murdered. The Kaidon, despite being a political ruler, is still very active in the military, even leading long time campaigns into enemy territory, leaving the elders to rule in his stead. Also, the next Kaidon is only elected after the current Kaidon dies.
Known Kaidon
State of Vadam