An Inevitable is a type of Outsider from The Clockwork Nirvana of Mechanus, an Outer Plane in the Planescape setting and several cosmologies in Dungeons and Dragons. They are the upholders of the fundamental rules of the multiverse, and track down and punish those who would seek to break them.
Creation and personality
Inevitables are made in great crèche-forges located in several locations throughout Mechanus. Here they are built through unknown ways and given intelligence. While they are technically Constructs, they are capable of learning and gaining a personality, though the process is slow.
After its creation, an Inevitable is given a target by a special set of Inevitables who divine the cosmos for any lawbreakers and is sent out to mete out justice. Upon their creation, they know nothing but how to use their abilities and their target. Given their lack of social skills, asking people for directions towards its target can be a very awkward affair. From its interactions with the world, an Inevitable begins to foster a personality, though as a being of Law this makes it at best a little unhinged and detached. They often get these personalities from hunting down several targets: the more they find the less of an automaton they become. However, the more independent they become, the more they long to return to their crèche-forge. When they do so, they have their personalities wiped and are given a new target.
Inevitables exist in several different kinds of models, each with their own specialty. It is not known if each individual crèche-forge makes only one model, or if several are made within the same facility.
Kolyarut are designed to uphold oaths both spoken and written. They appear like humanoid constructs made of black metal: they often have a half-finished look with many exposed parts jutting out here and there. Their heads often have their back exposed, and two glowing red eyes look forward from the skull (unless you were to consult the picture provided.)
Kolyarut track down oathbreakers and use intimidation, magic, or outright force to browbeat someone into upholding their bargain. They only kill if it is part of the bargain in question: otherwise they use spells like Suggestion or Geas in order to get the job done. Kolyarut hold all bargains to be equal in their importance: from the repayment of a monetary debt to the promise of an extradimensional horror to destroy the gods. They are the most talkative kind of Inevitable: they often speak with people in places where oaths are normally sworn, such as courts of royalty or law, temples and other such places. As such, they return back to their crèche-forges regularly.
They do not differentiate between those who have no intent on upholding their oaths, those who unwillingly broke their oaths or those who are not able to uphold their oaths for some reason. If possible, they first inform their targets of them being in breach: if they are willing to uphold their parts of the oath the Kolyarut will make sure they do so. Those less willing are made to uphold their bargain through force or magic. But if the Kolyarut discovers that both parties do not keep their ends of a bargain, it treats the bargain as void and dismisses it.
The most recognizable of the bunch (and the one who has existed the longest, dating back to the original Manual of the Planes), the Marut, is tasked with hunting down those who cheat death and granting them the end they escaped. As such, the enemies of the Marut are beings like liches, necromancers, cult leaders, extremely long-lived wizards, those who restore the dead back to live over and over (either willing like with adventurers or on a mass-scale on the unwilling, like necromancers).
Maruts are patient in their hunts, biding their time until they are ready to strike, where they strike targets with lightning-charged fists. Because of the solitary nature of many of their targets, Maruts have little opportunity to practice their social interaction, and as such are the slowest to develop personalities.
Maruts are large and broad, with heavy frames and strong limbs to better fight for justice with their bare hands. They have what looks like Greco-Roman inspired armor with huge axe-helmets that look like low tier Warrior armor from World of Warcraft.
In 4e, Inevitables as a whole were swept away; only Maruts remained, and they were initially given a backstory as astral mercenaries, before the Astral Sea sourcebook clarified that they were originally created at the dawn of creation by the gods to serve as the ultimate impartial arbitrators and enforcers. Dedicated exclusively to the promotion of law and order, Maruts in the Astral Sea serve as mercenaries to promote their vision, with the theory that they seek payment in reciprocal favors because they hope to eventually hold the entire multiverse in their debt, allowing them to reshape existence into something much more orderly.
The Quarut are tasked with delivering justice to those who meddle with time and relative dimensions in space, causing rippling effects and distort space and all kinds of other magibabble stuff you normally see on Doctor Who. The foes of the Quarut are potent indeed, and as such they keep their distance until they better understand their quarry. They often engage their foes by matter of proxies, interrogate associates and minions and seek weaknesses in their foes. While the Quarut are formidable in battle, the easiest way to deal with them is to determine what they want and fix the damage you've done. This is often easier said than done, and may require anything up to and including time travel to undo some calamity.
Quarut look like warped marionettes with slender brown frames and complex, green-gold plating. They tend to employ magic in order to gain the upper hand in battle, even spells like Wish and Time Stop in order to seize their targets. They seem to conveniently ignore the fact that the use of these spells is what they're created to combat.
The most potent and rare kind of Inevitable, the Varakhut are meant to uphold the divine order. All those who would seek to destroy the gods, or become one themselves, will eventually get into conflict with these potent beings. They are the most lethal of their kind, employing powerful magic and physical prowess in order to destroy their enemies. Those with a legitimate bid for godhood eventually come to blows with a Varakhut, but beings who only think they do are safe. While a Varakhut is powerful, it is likely no match for a god-to-be in single combat. Instead they aim at artifacts, followers and other sources of power or reverence for the wannabe-god.
There are only a few ways to stop a Varakhut: by destroying it, to ensure that you no longer have a bid for godhood, or by actually becoming a god. If one were to become a demigod or more, you become part of the order the Varakhut is sworn to protect, and as such are no longer a valid target. Varakhut look the most alien of the bunch: their bodies have sharp geometric shapes with elongated pyramids for arms. Instead of legs, the torso terminates into a single geometric point. The head is a flat disc on top of a slightly raised tube, giving an alien and inorganic appearance.
Zelekhut are centaur-shaped beings with porcelain skin, golden clockwork, mechanical wings and long, bladed chains that can extend from their forearms. They are tasked with hunting down fugitives of the law, to either bring them in for their proper punishment or, if deemed necessary, carry out the death sentence they escaped. For this they employ their long chains to disarm and incapacitate foes, then either use spells like Mark of Justice or Geas to ensure compliance. Failing that, they simply kill their quarry. They are the fastest Inevitables as well: their legs and wings allowing them superior speed to chase those who would deny justice.
Zelekhut take a more intense approach to their searches: they question passersby with impunity and will resort to violence if they think they are being held out on. More experienced Zelekhut observe those they have interrogated to determine if they were being lied to. Because of their frequent and intense interactions with people, they develop personalities the fastest of all Inevitables, and as such visit their crèche-forges very regularly.
Anhydrut, or Waste Crawlers, were a type of Inevitable in 3.5 splatbook sourcebook Sandstorm. Anhydrut's are charged with the sacred duty of hunting down and killing anyone who... tries to irrigate a desert. While this may appear surprising at first, one should consider that in many cultures, the expansion of a desert is seen as a vast threat. For a culture threatened by desertification, desert irrigation is a vast project, and large empires were once built entirely around irrigation systems (known sometimes as "water empires"). In this context, of course, an Anyhdrut makes a lot more sense.