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 referred 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."

Alignment
Jas is said to be the god of creation, because he made the raw materials of Gielinor (either alone or with the aid of other Elder Gods, which seems more likely). He is also believed to be god of power, as he owns one of the strongest objects known to Gielinor and the gods, the Stone of Jas. He would also need to have immense power because he would need to be powerful to even believe he is the god of creation.

In the Dragonkin journals, it is said that Jas cursed the Dragonkin to protect the stone. Kerapac, the creator of the Queen Black Dragon, is working on a way to free the Dragonkin from Jas' curse as he believes it makes them weak and they are not slaves. Kerapac also says at the end of the Journals that they will kill Jas.

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 with the same type of magical frequency. This is confimed to be a spot where the stone resided in the quest Ritual of the Mahjarrat.
 * 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, for, as stated before, RuneScape as a whole relies on Java to keep it running. This may also reference his massive powers, as mentioned above. It may also imply that Jagex may be the "god" that "created" RuneScape both in a physical sense and in-game.
 * In the fifth Postbag from the Hedge, the letter to the Chaos Elemental reads "Chaos Soahc, Jas. Hello?"
 * According to Kerapac's journals, the Dragonkin are studying a way to break the curse of Jas, and when they manage to do it, they will kill Jas. Although this seems unlikely since Jas is a God and far more powerful than the Dragonkin, after the Ritual of the Mahjarrat quest it is revealed when talking to a Guardian of Armadyl that the Dragonkin kept the other part of the Staff of Armadyl, meaning that they could use it to kill Jas.