Chieftain is a twist introduced in BB10.
The power of Chieftain allows the 2nd place finisher in the HOH competition to have plenty of power for the week. They will gain immunity for the week, unable to be nominated by the HOH. In addition, they will automatically compete in the POV competition, and will pick the 2 other houseguests to compete alongside the HOH, the 2 nominees, and themselves, replacing the random draw aspect of the POV competition. The twist ended at the Live Triple Eviction.
Effects on the Game
The Chieftain effectively removed the random draw aspect of Big Brother, allowing the houseguests to fully and completely control who would play in the POV, while also adding an incentive for houseguests to try and win that power in immunity for the week.
The Chieftain twist turned a lot of heads upon its introduction, but soon many saw it for what it was: a way to break the game by picking people for the POV and locking targets out of the POV with 100% assurance. This twist changed the backdoor strategy immensely, and for the entire time the twist was in play it was used to carry out backdoor evictions without fail every single time.