The Dustmen are one of the Factions that contest for the minds and souls of Sigilites in the Planescape setting for Dungeons & Dragons. An extremely weird blend of fatalism, nihilism, cynicism and Buddhism, the Dustmen believe in a principle of cosmic reincarnation between Life and Death - the thing is, they believe they, and everything else in the multiverse, is Dead.
Founded by the nihilistic lich Skall, the Dustmen argue that since suffering is endemic to all parts of the multiverse, clearly, the entirety of the known multiverse is some sort of grandly convoluted afterlife, using things like physical sensation and emotions to trick the souls trapped in it into believing themselves "alive"; as a result, they constantly die and then "anti-reincarnate" into this hellish afterlife over and over again. Only by accepting ones status as one of the dead and seeking to become as lifeless as possible can one hope to transcend this "False Life" and eventually attain the miracle of reincarnation into True Life. To this end, the Dustmen strive to be as stoic, bland and emotionless as possible, so much so that the undead actually tend to mistake them as being dead themselves. In fact, unbeknownst to the Dustmen, the highest members of their group are all undead.
The Factol's Manifesto strongly implies that this Faction may actually be a long-running ploy on Skall's part to ultimately build an army of the undead so massive he can forcibly extinguish all life throughout the cosmos. He genuinely believes the nonsense he's babbling about life being suffering, but that still makes it a con-job on at least some level. Fortunately, Skall gets himself Mazed during the Faction War.
Though they profess staunch neutrality, the Dustmen really don't like any of the other Factions, though the Doomguard and the Bleak Cabal are the closest to earning what passes for Dustman approval, given their mutually fatalistic outlooks on reality. Which is fair enough, as pretty much nobody likes them; it's simply the fact they don't go picking fights and their self-appointed task of collecting & disposing of Sigil's dead from their home base of the Mortuary that leaves the other Factions content to let them just get on with it.
The Dustmen's membership is predominantly comprised of humans, tieflings and half-elfs, especially those with planar backgrounds - this isn't due to prejudice, just that the philosophy of the Dustmen tends to be most appealing to races with particularly short and/or hard lives. As mentioned above, they all benefit from what the Dustmen call the Dead Truce, which compels mindless undead to ignore them, but what they keep secret is that they can also gain the power to command undead as if they were a Neutral Cleric once they reach the 4th Circle. The downside to membership is that, of course, any raise dead type effects have a flat 50% chance of failing.
By the ninth day of the Faction War, Skall has been Mazed by the Lady of Pain, although his loyal followers instead believe he's achieved True Death. They stay mostly out of the conflict, and like the Bleak Cabal they simply shrug, divest their organization of official ranks, cease even their meager attempts at proselytizing, and just carry on with their work.