Dagannoth are sea monsters. Many are found near areas inhabited by the Fremennik, who call them daggermouths and hunt them for their skin, which is used to make armour. There are many types of Dagannoth, the most powerful being the three Dagannoth Kings. Dagannoth are assigned by Chaeldar, Sumona, Duradel/Lapalok and Kuradal as Slayer tasks. The Balmung (as well as its upgraded form), released with the quest Blood Runs Deep, hits them very hard, similar to the effect of using Keris on Kalphites or Scabarites.
Little is known about the origins of the dagannoth species. Dagannoth are first documented in Third Age where they started attacking the Fremennik, causing great losses to them. The Fremennik people battle them to this day.
Through the Spirit Dagannoth they reveal their goal: To force the entire surface world to be plunged into the Deep through a terrible flood, the event is called "The Day of Rising" by the Dagannoths. The lucky ones will be consumed first by the Dagannoth while the others will drown before they are also consumed.
There are several types of Dagannoth, which vary by level, location and occasionally name. For information on a specific type of dagannoth, see its article.
- In the FunOrb game Armies of Gielinor, one may summon a Dagannoth. Jagex has used the image of the Spirit dagannoth to illustrate this.
- Dagannoth may be based on the Deep Ones from H.P. Lovecraft's The Shadow Over Innsmouth. In the aforementioned story, they worshipped the elder beings Father Dagon and Mother Hydra.
- Dagannoth may also be based on the Xenomorph Aliens from the Alien movie series, as several references are made to them throughout the game.
- While the idea for the creatures characteristics may derive from the above mentioned, the name itself seems as if it may come from one of the first computer role-playing games, Dungeons of Daggorath, produced by DynaMicro in 1982.
- These are one of three 'Animals' in RuneScape, that show previously unknown militant qualities, the others being Monkeys and penguins.
- The Dagannoth Kings have a long distance attack, similar to the Kalphite Queen, King Black Dragon, Chaos Elemental, and Revenants.
- They may be dinosaurs; while fighting the Dagannoth Mother from Blood Runs Deep, a music track called "Maiasaura" unlocks, which is the name of a genus of dinosaur known especially for their maternal nature.
- The plural of dagannoth is dagannoth, which can be seen when receiving a slayer task for them.