Demon is a monster type in ADOM. Most of monsters with type have also secondary type, such as humanoid, construct, etc.
Demons are uncommon monsters that include some of the most powerful monsters in the game. Apart from molochs and least daemons, most demons have corrupting attacks and/or magical powers such as an elemental breath weapon.
Almost all members of the demon monster type are represented by the '&' symbol; though some constructs (grues) and 'I' represented monsters (quasits, imps) may also belong to the group. The category includes all elemental demons, molochs, greater molochs, balors, greater daemon; and the fearsome boss monsters the Emperor Moloch, the greater balor, and Andor Drakon.
Demons are vulnerable to the aptly named arrows/quarrels (and sling bullets as of 1.2.x) of demon slaying. Additionally, several artifact weapons in the game slay demons — including the Trident of the Red Rooster, the Rune-covered trident, Executor, Purifier, Justifier, Grod and Vanquisher.
Furthermore, blessed weapons and missles deal 1.5 times their base damage to demons. This stacks with slaying — meaning that blessed arrows or quarrels of demon slaying come in exceptionally useful in D:50 or against all types of molochs.