Demons are a class of creature including a number of very similar races; many are characterised by a mix of human and beast-like features, often in hellish black or red colours.
Demons usually come from other realms, such as the Infernal Dimensions and Abyss and most are servants of Zamorak or Zaros. With the release of the Demon flash mobs and Mod Osborne's comments, it has become clear that demons can sense that the gods have a greater influence on Gielinor "they're sniffing in the air, and they can smell a change is coming", this is further evidenced by Ux's ability to sense things after The World Wakes (as is shown in the The Book of the Godless). They are generally considered to be fairly strong, except for imps, and have low defence and strength. Imps fight by using melee, but more powerful ones can also use magic. Demons usually fight barehanded, save imps and some of the most powerful demon generals. The ability to slay stronger and stronger demons is often a personal landmark for many players. Demons are especially weak towards ranged but stronger against melee attacks. The magical swords Silverlight and Darklight, , are enchanted to be especially effective against demons. Holy Water is a powerful ranged weapon against demons.
Most players believe that demons ranging from Lesser demons to Black demons have relatively poor drops when killed, so it is not recommended to kill these for any purpose other for than Slayer task or by medium level player seeking combat experience. Other players believe that lesser and greater demons can be profitable if they can be killed quickly and their common 300+ coin weapon drops cashed in with High Level Alchemy, and even a few players can be found training against the powerful black demons. Black demons, Nechryaels and Abyssal demons can be profitable if the player banks their Infernal ashes, since they are a 100% drop and are used for Prayer training. Most players agree that demons known for worthwhile drops are Tormented demons, Abyssal demons, K'ril Tsutsaroth, and Nechryael, although all of these are either hard to kill or require immensely high requirements such as 80+ slayer or completing many quests with very high stats.
With 11 different bosses, Demons are some of, if not the most common quest bosses.
According to Evil Dave, Hellrats are demons and are the lowest form of demon, weaker even than imps. Players cannot kill hellrats, but pet cats can.
Reldo in Postbag from the Hedge reveals that all demons have true names. They do not reveal their true name, however, because "names have powers". Demons that reveal their true names are usually so powerful that the name cannot bind them anymore; K'ril Tsutsaroth is an example.
True demons used to drop Ashes as their 100% drop. After an update, they now drop corresponding ashes of their type (Imps, Icefiends and Pyrefiends drop Impious ashes; Death spawn, Greater Demons and Lesser demons drop Accursed ashes; and Abyssal demons, Nechryaels, Black demons, Demon bosses, Tormented demons, the three demons from the Underground Pass and K'ril and his bodyguards drop Infernal ashes).
In Armies of Gielinor, a Jagex game on the website FunOrb, you are able to summon greater demons. They are considered Zamorakian, require level 4 favor with Zamorak to summon, and have 45 Strength.
Abyssal demons are known to be demons. Other denizens of the Abyss (Abyssal leeches, walkers, and guardians) are strange-looking like Abyssal demons, as well as dropping ashes. It is believed that the other denizens are not demons (although Holy water and Silverlight/Darklight have not been tested against them). There is one known difference between Abyssal demons and other Abyssal denizens: the Abyssal demons do not drop Abyssal charms.
Prior to the Evolution of Combat, Lesser, Greater and Black demons were agressive and attacked with melee.