The dark folk

The "dark ones" or "dark folk" are humanoids that first appeared in the old Fiend Folio. They were converted to 3e by Tome of Horrors and from there they received a fair amount of expansion in other 3pp.

In 4e the dark folk were native to the Shadowfell, which may remain the case in 5e.

Pathfinder presents dark folk as humanoids with the (dark folk) tag, claims their ancient name for themselves if "caligni," endemic to the Darklands (Underdark), and explains that they worship shadow beings called "owb." Paizo seems to really like the dark folk.

Various supplements have introduced variants and related monsters:

• The Tome of Horrors series introduces the dark creeper, dark stalker, and huggermugger.
• The Pathfinder Bestiary series introduces the dark caller, dark dancer, dark empath, dark slayer, and the owb.
• Behind the Monsters: Dark Folk from Fat Goblin Games introduces the dark keeper.
• Monster Menagerie: Lurkers in the Dark from Rogue Genius Games introduces the dark dweomerthief, dark piper, dark reeker, dark regent, dark tatterdemalion, and dark hound.
• Creature Codex for 5th Edition from Kobold Press introduces the dark eye, dark servant, and dark voice.

The dark folk are a minor yet fascinating monster family, and I should like to explore them further in the future.