Denizens are immortal people created from Nothing and made by the Architect who said they have to record the actions of mortals in the Secondary Realms. A specific 7 Denizens are the trustees of the house, also known as the morrow days.
Denizens are similar to humans in all aspects but these:
- The blood of a Denizen is blue with two unexplained exceptions, while the bones are golden.
- Denizens are very resistant to change of any kind, and are often described as narrow-minded or stupid.
- Denizens are naturally good-looking. Additionally, if a Denizen’s House Precedence is high, he or she is better-looking and taller than Denizens of lower precedence.
- Denizens are nearly immortal:
- Denizens cannot die of old age, sickness, dehydration, or starvation while in the House, and will eventually heal from almost any injury, including decapitation. Denizens normally value sicknesses from the Secondary Realms. If their body is destroyed, they can slowly grow a new one, though they can be prevented from doing so. The ability to survive without food or drink while within the House, as well as not dying from old age, extends to Mortals and Piper's Children, although the resistance to injury does not.
- Denizens can only be killed by:
- Fire, superheated steam, or other sources of extreme heat;
- Certain weapons (such as the Commissionaires’ Clubs and various weapons used by the Glorious Army of the Architect);
- A prolonged absence of their heads; without sorcerous intervention
- A festering bite or scratch from a Nithling, which dissolves them into Nothing;
- A Key;
- Drowning (although, this does not completely kill them immediately); and
- Falling from at least 15,000 feet.
Denizens are all ranked in precedence within the House, and are often asked their precedence when being commanded by a superior Denizen. The ranks goes from 1 to an unknown number, presumably in the hundreds of millions or in the billions. The highest number recorded in the series was Pravuil as a Coal Collater, rank 9,665,785,553 (it is unknown whether this is his true precedence as he has been seen to serve Saturday/Sunday in Superior Saturday). The more important Denizens or Piper's Children have lower precedences. An example for this is in Mister Monday when Suzy Turquoise Blue is an Ink-Filler 6th class, her precedence is 182,367,542. In Sir Thursday Arthur's precedence is 6 (which confuses the recruiting officer who comes to collect Arthur, who "thought perhaps there were a large number of zeroes missing") after defeating Mister Monday, Grim Tuesday, and Drowned Wednesday. The only people with greater precedence within the house being The Architect and the four remaining trustees.