Jas

Jas is a mysterious being of which extremely little is known. Believed to be an Elder God, he seems to have existed even before Guthix had arrived on the plane of Gielinor, possibly even being its true creator. His only remaining legacy is the mythical Stone of Jas, a powerful magical artefact that illustrates the great might he must have, probably surpassing even Guthix's power.

Most of what is known of Jas comes from the following quote from the While Guthix Sleeps quest log, which confirms not only that he is a being, but also that he is either male or genderless, since guthix is also genderless but refered to as he:

"I've seen a vision by touching the strange orb. It has communicated to me that it is 'The Stone of Jas', owned by Jas, and protected by creatures he has enslaved for the purpose - the Dragonkin. One of the first of the Fremennik tribe touched the Stone and it changed them drastically...this is how they became Lunar mages."

Trivia

 * The imprint in the centre of the Fist of Guthix cavern bears a strong resemblance to the Stone of Jas and according to Movario's notes, resonates the same type of magical frequency.
 * JAS is a real-life acronym which stands for Java Application Server, the application that drives Runescape's game engine. This may imply that Jas is some sort of elemental godly being, necessary for the existence of Gielinor. This may also reference his massive powers, as mentioned above. It may also imply that Jagex may be the "god" that created RuneScape.
 * In Post Bag form the Hedge, PostBag 5 in the letter to the Chaos Elemental, it says "Chaos Soahc, Jas. Hello?"