Phourkyn One-Eye was a sunwyrm posing as a human wizard in Thentia during the Rage of Dragons of 1373 DR. The wizard Firefingers believed that there had once been a real Phourkyn One-Eye until the sunwyrm killed him and took his place.
In 1373 DR, posing as Phourkyn, the sunwyrm infiltrated a cabal of humanoid wizards in Thentia who were studying the Dracorage mythal. He tried to disrupt their research using all means and regularly informed Sammaster of their progress. After the avariel Taegan Nightwind correctly inferred that the wizards' draconic ally, Samdralyrion, attacked them not just because of the Rage but because one of their number was a traitor, Phourkyn decided to adopt a more active approach to kill the wizards. He summoned a chasme, binding it to him to increase not on his own strength but that of the demon as well, and sent it to kill the other wizards.
When Taegan and the faerie dragon Jivex intervened to defend them, Phourkyn initially tried to use the Chasme to lead them to suspect other wizards of being the traitor. When they refused to take the bait, he instead captured them and took control of their minds so that the next time a dragon showed up, Taegan would cast the spell to incite it into a Rage. When the elven wizard Rilitar realized something was amiss and removed the enchantment before Taegan could finish the spell, Taegan revealed Phourkyn as the traitor. With his cover blown, Phourkyn assumed his draconic form and attacked them directly. With the help of the other wizards, Taegan and Jivex killed Phourkyn, though the sunwyrm managed to mortally wound Rilitar before he died.