History Main / RuleOfTwo

* ''Franchise/StarWars'' is the {{Trope Namer|s}}. The Sith have the Rule of Two, where there can only be a Sith master and an apprentice - no more, no less -- one to possess power and the other to desire it. The idea is that each Sith Lord teaches one apprentice until they are strong enough to destroy the master and take their place, at which point the apprentice will take on a student of his own, or until the master kills the apprentice and gets a new one. In this manner, each master not only ''becomes'' strong, but must ''stay'' that way to stay alive, and each student must become stronger than their master. A master cannot have more than one apprentice, because they may team up to kill their master despite being individually weaker than them, then turn on each other and weaken the Sith Order. In short, ChronicBackstabbingDisorder as a way of life and a code of morality. (Although this didn't always work, because it was shown with Sidious, he killed his master while he was sleeping.)

* ''Franchise/{{Gundam}}'': Every [[GloriousLeader dictator]] in the franchise usually has an AcePilot enforcer (often also a CharClone) backing them up. Given ''Gundam'''s military themes, a series may also have a chain of these.

** Everyone have a counterpart (not necessarily yin-yang or dark side): [[{{miko}} Reimu vs Sanae]], [[{{Catgirl}} Chen vs Rin]], [[CuteWitch Marisa vs Alice]], [[YourVampiresSuck Remillia vs Flandre]], the list goes on and on...

* ''Franchise/StarWars'' is the TropeNamer. The Sith have the Rule of Two, where there can only be a Sith master and an apprentice - no more, no less — one to possess power and the other to desire it. The idea is that each Sith Lord teaches one apprentice until they are strong enough to destroy the master and take their place, at which point the apprentice will take on a student of his own, or until the master kills the apprentice and gets a new one. In this manner, each master not only ''becomes'' strong, but must ''stay'' that way to stay alive, and each student must become stronger than their master. A master cannot have more than one apprentice, because they may team up to kill their master despite being individually weaker than them, then turn on each other and weaken the Sith Order. In short, ChronicBackstabbingDisorder as a way of life and a code of morality. (Although this didn't always work, because it was shown with Sidious, he killed his master while he was sleeping.)

* In ''Series/{{Heroes}}'', the Company's rule is "one of them, one of us" -- "them" being a human with some mutant ability, and "us" being a {{Muggle}} whose first loyalty is, always and forever, to the Company.

* In the Rome, this began with the rule of two consuls in the diarchy. And was revived by Emperor Diocletian creating the ranks of senior emperors - the Augustus - and junior emperor - the Caesars. This was then squared by implementing the Tetrarchy, which ended after the Civil Wars of the Tetrachy and Constantine the Great ultimately becoming a single Augustus.

** Since ''WesternAnimation/StarWarsRebels'' has canonized the Imperial Inquisition, they are Dark Side Force-sensitives employed by Darth Vader, but are immune to the Rule of Two because they are not Sith. They're purposely trained so as not to reach the power level where they'd run the risk of violating the rule like Asajj Ventress did.[[note]] However, this resulted in the Inquisitors having significant weaknesses of their own: since they were trained to not reach the power level of a true Sith, they're able to take out Jedi that were isolated or weak enough to not in the path of Order 66, but when confronted by prepared and skilled Force-users such as Kanan, Ahsoka or Maul, the Inquisitors are usually defeated quite handily.[[/note]]

** Ultimately Darth Bane's philosophy, while it kept the Sith alive in secret for millennia, also resulted in the order's undoing, as the chain could be easily broken by a factor that Bane failed to take into account-[[EvilCannotComprehendGood the potential redemption of either the master or the apprentice]]. Darth Vader's RedemptionEqualsDeath and, in the old ExpandedUniverse, Jacen Solo/Darth Caedus' apprentice renouncing the Dark Side of the Force and the Sith shortly after the former's demise, pretty much spells the end for the Sith Order ''because'' of the Rule of Two. What's worse is that Bane really should have known better. The Sith Lord whose Holocron gave Bane the inspiration for the Rule of Two, Darth Revan, had also renounced the Dark Side, and Bane knew this.
*** ''Film/TheLastJedi'' exposes another flaw in the Rule of Two related to the redemption example above - [[spoiler:a Sith apprentice killing his master but deciding to destroy the entire Sith doctrine out of some sort of principle. While Snoke was not a Sith lord, Kylo Ren still betrayed him, and comes to the realization that both Jedi and Sith doctrines are intrinsically flawed, and that the past should be let go of... By being destroyed completely.]]
** The rule didn't make it intact through Bane's own lifetime. By the time his apprentice confronted him he had already taken a second, and she had started training one of her own. Zannah's apprentice ended up wandering off and doing his own thing as a Dark Side user who isn't ''technically'' a Sith. While after killing Bane, Zannah took his second apprentice (who proved far more promising than the candidate she'd found) as her own.

* In ''Manga/{{Naruto}}'' there's Kabuto and Orochimaru. Then there were Zabuza and Haku.
** [[spoiler:Madara and Obito, started like this but Madara died shortly thereafter leaving all the work on Obito and when Madara revived, they became BigBadDuumvirate.]]

* The villains ''Series/KamenRiderRevice'' could be seen as one long chain of this. The Chameleon Deadman is the personal enforcer of Olteca, who [[TheManInFrontOfTheMan feigns being]] TheDragon to [[PuppetQueen Aguilera]] while really serving [[spoiler:Hideo Akaishi]], who himself serves [[AncientEvil Giff]]. Aguilera also has Julio as her most loyal (and [[spoiler:after #16, only]]) minion.