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->''"Always two, there are. No more. No less. A Master and an apprentice."''
-->-- '''Master Yoda''', ''StarWars Episode I: The Phantom Menace'', about the Sith

Sometimes the BigBad gets bored doing everything himself. He'll get a [[TheDragon second in command, a lieutenant, or an apprentice]] to keep things interesting. This is the RuleOfTwo. There are two big bosses, and both have to be taken down.

It's usually understood that the two want to keep it that way. Never introduce a third, and quickly replace the other if they go down. Due to infighting or general ForTheEvulz culture, the BigBad may [[YouHaveOutlivedYourUsefulness decide to dispose]] of {{the Dragon}} himself and get a new one. Similarly {{the Dragon}} [[TheUsurper will overthrow]] the BigBad if the opportunity presents itself, and bring on a new Dragon of his own. The tension of this dynamic is that they rely on each other, but both know it's a race to see who will stab who in the back first.

TheHero is usually the prime candidate for the replacement. If TheHero is about to take {{the Dragon}} down, expect the BigBad to try to turn him to TheDarkSide. If {{the Dragon}} is about to take the hero down, expect him to [[WeCanRuleTogether offer an alliance]] to overthrow the BigBad and take his place. Compare and contrast BigBadDuumvirate, DeceptiveDisciple and BastardUnderstudy.



[[folder:Anime and Manga]]
* In ''Manga/{{Naruto}}'' there's Kabuto and Orochimaru. And it should be noted that the Akatsuki only move in pairs. Then there were Zabuza and Haku.
** [[spoiler: Madara and Obito could be this due to current events.]]
** [[spoiler: Kaguya and Black Zetsu.]] Although the dynamic isn't really there since [[spoiler:Black Zetsu is the one calling the shots, as [[FlatCharacter Kaguya has absolutely no personality at all]].]]

[[folder:Fan Works]]
* [[MadScientist Thunderstorm]] and [[KillerRobot Shadow]] in [[Recap/CalvinAndHobbesTheSeriesS3TVM2Thunderstorm the one TV movie they appear in]] easily fit this in ''Fanfic/CalvinAndHobbesTheSeries''.

* ''Film/CrouchingTigerHiddenDragon'': The apprentice (Jen) is a more skilled combatant than the Master (Jade Fox), but the Master is more treacherous.
* ''Franchise/StarWars'' is the TropeNamer. The Sith have the RuleOfTwo, 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. Each generation of Sith is stronger than the last, because any weak link in the chain is dead. A master cannot have more than one apprentice, because they may team up to kill their master despite being individually weaker than him, then turn on each other and weaken the Sith Order. In short, ChronicBackstabbingDisorder as a way of life and a code of morality.
** The origins of this rule are explained in ''Literature/DarthBane: The Path of Destruction'', where the Sith have become rife with in-fighting due to hordes of individuals claiming the title of "Dark Lord of the Sith" with a leader pretending to be just a first among equals. The Sith philosophy in such a climate can only lead to self-destructive power struggles that serve only to empower their enemies. [[VillainProtagonist Bane]] eventually comes to the conclusion that there should only ever be two Sith Lords at a time: one to hold power, and the other to covet it. Eventually the apprentice should take it by force when they're ready. Furthermore he concludes the Sith should not work for the fall of the Jedi and to conquer the galaxy by armed conflict, but rather subtlety, which Palpatine eventually pulled off. [[spoiler: Having made up his mind on this, ''Darth'' Bane makes sure all the collectivist Sith Lords unintentionally commit collective suicide.]]
** Interestingly, the ExpandedUniverse reveals that Palpatine, Dooku, Vader and other Sith Lords had their own minions trained in the dark side; the rule wasn't technically broken because they weren't "true" Sith Lords, but mere warriors or spies with some lightsaber training and ability in the force. However, it seems that once a minion begins to grow too strong, or - worse - is discovered being trained in the Sith arts, ''one of them has to die'', be it minion or master. Or potentially the apprentice, with the minion becoming the new apprentice.
*** Palpatine, for example, deceived his own master into thinking that Darth Maul was simply an assassin, not a true apprentice. The one thing that didn't go according to plan was that Maul was defeated right after Palpatine disposed of his own master...though Palpatine [[XanatosSpeedChess made that work to his advantage]] by recruiting Dooku, who was better suited than Maul had been for the very public role needed in the next phase of the plan.
*** Conversely, Palpatine began to suspect that Dooku was plotting the same in ''WesternAnimation/StarWarsTheCloneWars'' with his own assassin, [[DarkActionGirl Asajj Ventress]], and ordered him to have her killed to prove his loyalty. Dooku followed through with the order but failed to have her killed, resulting in her turning on him.
*** Darth Tenebrous broke the rule by recruiting two apprentices ''and not telling them about each other''. After Darth Plagueis "took over", he was surprised by Darth Venamis, who had learned of him, was better at the use of the lightsaber and had been trained in Plagueis's style. [[spoiler: Plagueis was smarter, imprisoning Venamis and experimenting on him for years.]] It's possible that Venamis wasn't a "true Sith" though.
** 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.
*** It's revealed in the season 2 finale that despite having immense rage at the Sith Order as a whole for betraying and discarding him, [[spoiler:Maul]] still adheres to this philosophy. And he's looking to corrupt [[TheHero Ezra]] into becoming his apprentice.
** Ultimately Darth Bane's philosophy also resulted in the Sith's undoing, as Bane did not take into account [[EvilCannotComprehendGood the possibility that either the master or the apprentice could actually be redeemed]], as evidenced by Darth Vader's RedemptionEqualsDeath and Jacen Solo/Darth Caedus' apprentice renouncing the Dark Side of the Force and the Sith shortly after the former's demise. 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.

[[folder:Live Action Television]]
* 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.

[[folder:Video Games]]
* This is a recurring motif in ''VideoGame/{{Touhou}}''.
** BigBad and her one-and-only [[TheDragon dragon]]: Remillia-Sakuya, Yuyuko-Youmu, Yukari-Ran, Kaguya-Eirin, Eiki-Komachi (not bad folks), Kanako-Sanae, and so on.
** 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...
** Characters fight in pair during ''Imperishable Night''.
** Yukari Yakumo's ability is explicitly defined as the ability to manipulate border between ''two'' different things. As for what that means in practice, it apparently means [[RealityWarper whatever Yukari wants it to mean]].
** For that matter, the yin-yang features heavily in ''VideoGame/{{Touhou}}''; it's even one of Reimu's attack mode.
* In ''VideoGame/BatmanArkhamAsylum'' and ''VideoGame/BatmanArkhamCity'', the Joker keeps Harley as his right hand girl. Even if she's not very good at it.
* Prominent in ''VisualNovel/FateStayNight''. Sure, you could just kill the Master and run away from the Servant (it's even repeatedly stated to be the best strategy), but nobody ever does. Most apparent with Kotomine/Gilgamesh and Kuzuki/Caster. Nobody in either pairing is really the boss. Gilgamesh will do what Kotomine says, if he feels like it. Caster would obey Kuzuki's orders, but Kuzuki is too passive to really bother most of the time. Also apparent in Kotomine's fight against True Assassin and Zouken Matou. [[spoiler:He's stronger than Assassin, but can't kill him due to him being a Servant, so he has to take out Zouken first and ''then'' Assassin would be vulnerable. But Zouken is essentially unkillable by normal means plus Assassin is keeping him busy.]]
* The two major villains of ''VideoGame/MarioAndLuigiSuperstarSaga'' are BigBad Cackletta and TheDragon Fawful. In ''[[VideoGame/MarioAndLuigiBowsersInsideStory Bowser's Inside Story]]'', where [[DragonAscendant Fawful is the Big Bad]], he gets a Dragon of his own, Midbus.

* In ''[[http://evilplan.thewebcomic.com Evil Plan]]''. Dr. Kinesis hires Alice as his second in command [[spoiler: because he loses his previous number two]].

[[folder:Western Animation]]

* This is a common theme in ''WesternAnimation/KimPossible''. Drakken and Shego, the Seniors, and even Gemini says that he was saving the "Alpha" title for someone special.