Ux is a demon travelling with the adventurer Kara-Meir. Like most demons, he originates from the Infernal Dimensions, and was previously bound to the demon pact, a contract instated by the god Zaros to recruit demons to his will. However, he was somehow able to break free of this pact, and wishes to take up arms against the gods Zaros and Zamorak[1]. He started travelling with the adventurer Kara-Meir to try and achieve this, and is currently heading towards the town of Lumbridge, as a portal there was giving him a headache.[2]
The portal was later revealed to be Zamorak's doing, and his way of entering Gielinor again. It is unknown why Ux had a headache or why he did not appear at the Battle of Lumbridge, despite travelling there with Kara-Meir.