Jas is a God mentioned only directly by name in Melzar's notes and by the Chaos Elemental in the Postbag from the Hedge. One of the one-liner responses from the Oracle is "Jas left a stone behind," one of the few serious statements she makes. Jas is also mentioned by the player during Temple of the Eye.
She is responsible for the creation of the Stone of Jas which was used to curse the Dragonkin, sending them on murderous rampages against human settlements. It was also used to create the Rune essence mine and Astral Altar. The Stone of Jas also resulted in the formation of Daeyalt ore in the Meiyerditch mine. But its full power wouldn't be recognized until later on in the 3rd age, when Zamorak found out about the Godsword's whereabouts and, in a final attempt to bring out his ultimate victory, used the Stone as a source for his most powerful spell, immediately wiping out the entire area previously known as Forinthry (The Wilderness) and effectively ending the God War due to Guthix being awoken by the blast. The Stone's location is currently unknown but was cited in Sins of the Father by Drakan's sister.