Tseleth was a Human Dreamwalker that turned on the Order in its darkest hour. In penitence for his cowardice, he exiled himself to the Sea of Fire, hoping to take his own life. Instead, he came upon the fabled city of Bir Mahallah and, through circumstances unknown, became favored of the Lornon Arkati Luukos. He came to the Solhaven district of Vornavis during the events of Ride of the Red Dreamer. While largely seeking to aid Vornavis against the threat posed by Indhis, he took advantage of the chaos in the city to enforce Luukos's interests there and explore his own fondness for creating life. These efforts culminated in the creation of the abomination Athamael.
After a long absence, Tseleth returned to Solhaven to request assistance from the townfolk in order to reclaim the Sanctum of Scales, the home of his Luukosian sect. It had been corrupted by the Eye of Goseth, an Ur-Daemon artifact. After discovering that the corruption was irreversible, Tseleth returned to the Maw of Luukos and has not been seen since.
You see Tseleth the Infernal. He appears to be an Arch Lich. His form is towering and skeletal. Emerald flames belch forth from the depths of the eyes sockets in his skull, the charred skin of which has torn to reveal glimpses of blackened bone. A half-molten crown of gold, inlaid with cracked emeralds, is fused to his skull. Viridian flames rage beneath his exposed ribcage. Ebon-taloned wings draped in tattered, leathery flesh sprout from the fire-ravaged bones of his back. He is wearing a pulsating chrysochlorous soulstone suspended from a gilded chain, the charred and ragged remains of a dark hooded greatcloak, some ragged strips of burnt cloth, and a stygian wristlet forged from heavy ora links.