Tzadikim Nistarim

""And the Lord said, If I find in Sodom 50 righteous within the city, then I will spare all the place for their sakes.""

- The Bible

If numerous works of fiction and even religion are to be believed, then in this world are a number of people whose mere existence keeps the universe going. Maybe because the gods are paying them particular attention and these few people are effectively acting as the scale by which the rest of the world is being judged. The origin of this idea is the Tzadikim Nistarim, or Lamed Vav Tzadikim, a concept rooted in Judaism which states that the world continues to exist only because of the existence of thirty-six Righteous Souls, who keep the whole thing going. The idea exists in other religions also, but this is the one which is most widely known.

There are several characteristics which are essential for a person to be a member of the Tzadikim Nistarim:
 * They're kind of like a sample number for God within an entire population: So long as these thirty-six are good and true then the world is safe, even if absolutely everyone else has descended to barbarism.
 * They have mystic powers, possibly very obscure mystic powers of which they are mostly unaware, given that:
 * They can never know who they are. If any of the Tzadikim Nistarim ever realizes or uncovers their identity, they will die soon after and be immediately replaced. (So being a Chosen One is not necessarily the same as being a member of the Tzadikim Nistarim, though they may be). Killing one of them may bring about The End of the World as We Know It, but not necessarily.
 * They may or may not take an active stance in protecting the world on a daily basis. The theory is that these people, via their mere existence and the virtues they have, are enough to keep the world from going to hell in a handbasket.

The actual concept of this may be covered in Save This Person Save the World. Also, lots of messianic characters are going to fit here. Especially those with Incorruptible Pure Pureness. Another requirement should probably be dying a natural death, since killing one of the Tzadikim Nistarim brings about The End Of The World As We Know It.

Just for Fun, this rule can be applied to characters in fiction. Sometimes it's even been outright utilised by creators in the fiction itself.

Anime and Manga

 * Yugi Muto of Yu-Gi-Oh!. Most likely the regular one in particular, since The Other Yugi has technically been dead for thousands of years, and it's only via the regular Yugi's existence that he can continue to exist and thus save the world multiple times. Regular Yugi is often described as "the chosen one" or "vessel" for the Other Yugi.
 * Monster: Dr. Kenzo Tenma. Who does what he perceives to be the moral and right thing, at the expense of his reputation.

Comics

 * The Sandman: According to Death of the Endless, Joshua Norton was one. He stopped a riot trying to burn down chinatown by dropping to his knees praying loudly, Shaming the Mob.

Literature

 * André Schwarz-Bart's classic novel The Last of the Just uses the legend of the Tzadikim to frame a tale of Jewish persecution and survival through eight centuries in Europe.
 * Young Wizards: Diane Duane clearly used this concept as the basis for the Abdals in the series. There are more than 36 of them, but only because they exist in numerous realms of habitation (some of which are probably far stranger than planets) throughout the multiverse. In relative terms, they're still very rare, and our planet probably has considerably fewer than 36. In all other respects, they're pretty much identical to the Tzadikim Nistarim.
 * Jodi Picoult mentioned them in her book, Keeping Faith, in which is the eponymous character was believed to be one.
 * The 1988 novel The Quest for the 36 by Stephen Billias.
 * Sam Bourne's book The Righteous Men is centred around a plot to kill the Tzadikim Nistarim and thus end the world.
 * No modern examples of the 36 exhibited mystic powers, but they each help out their fellow human beings, from one performing individual acts of kindness to neighbours, to another who blackmarkets a medication for HIV that will help millions around the world.
 * Sometimes some subconsciously try to obscure their altruistic nature so much that they are often criminals due to fate or in their attempts to help others. One member of the 36 did become aware of his nature, and did not die instantly however. Additionally one member of the 36 at a time is determined to be the Messiah if the End of Days occurs while he is alive, and a particularly spiritual and pure Righteous Man will attract others to him, and even be able to recognise his fellows.
 * Members of the 36 mentioned include a pimp who sold all his belongings to save a woman from entering prostitution, a medieval pimp who could pray for rain, a teenage hacker who invents a virus that will eventually destroy all child pornography on the internet, and a simple nurse in Africa who saves war refugees

Live Action TV

 * Buck Rogers in the 25th Century: borrowed a variation of that idea for one of the second season episodes.

Tabletop RPG

 * Referenced in Unknown Armies, wherein a street level rumor claims that if there are ever less than nine truly righteous men left in the world, God will destroy it.

Web Comics

 * Whoever they are, we have it on good authority that Cleo from Bobwhite is not one of them.

Web Original

 * Global Guardians PBEM Universe: The Tzadikim Nistarim really exist (along with pretty much every other legendary figure) because of the power of human belief. In the GGU, if enough people believe something is real, it becomes real. Some of the 36 are real people, others are Anthropomorphic Personifications of certain ideals.