Zmodlor was a minor demon who specialized in infiltration.
Zmodlor once possessed a schoolhouse in the village of Jortas with the eventual goal of sacrificing the children to obtain far greater power. The Guardian Aegwynn discovered his activities and banished him back to the Nether.
With this goal in mind, he recruited both orcs and humans who were prejudiced against one another into a new incarnation of the Burning Blade cult. As an incentive, he promised to help his new followers destroy their enemies whether they were humans who hated orcs or vice versa. Zmodlor and his followers (none of whom were aware that Zmodlor had recruited members of the very race they were attempting to wipe out) did everything they could to exacerbate tensions between the two states. While Zmodlor oversaw all of this, he discovered that his old enemy Aegwynn was still alive. He was able to imprison both her and Jaina Proudmoore within magical wards, but only temporarily.
Among the members of Zmodlor's Burning Blade were advisors to both Jaina Proudmoore and Thrall: Kristoff, Jaina's chamberlain, and Burx, one of Thrall's chief warriors. Kristoff was convinced that Thrall was the only civilized orc in existence and that if he ever passed away, the orcs would "revert to type" and overrun Theramore. Burx had grown up as a slave to humans during the Lethargy of the Orcs, and had been abused by them every day of his life until his liberation by Thrall--Burx, therefore, despised all humans. When Kristoff found himself on Theramore's throne following Jaina's disappearance, he ordered Northwatch Hold reinforced, even though a buildup of soldiers at Northwatch would be viewed as an act of aggression by the Horde. When Thrall heard of the influx of troops at Northwatch, Burx convinced Thrall to send him to investigate, and to give him command of an army. Between them, Zmodlor's two puppets succeeded in starting another conflict between orcs and humans, as when Burx arrived at Northwatch he gave the humans an ultimatum: either dismantle the entire keep and vacate the land in one hour, or be slaughtered.
Zmodlor's plan would have succeeded, but for Jaina and Aegwynn's timely escape from his prison. Jaina returned to Theramore and dealt with Kristoff, inadvertently killing him. Once she learned of what had happened during her absence, she contacted Thrall, who was able to get to Northwatch in time to cut the battle short. After using his elemental powers to command the attention of all present, Thrall rebuked his soldiers for their behaviour and ordered them to stand down. Burx was executed on the spot for his treachery.
Meanwhile, Jaina and Aegwynn confronted Zmodlor and several of his worshippers atop Dreadmist Peak. Zmodlor was banished by Aegwynn's spell, cast by Jaina Proudmoore, moments before his plan would have succeeded. Aegwynn remarked that this was the last Azeroth would see of Zmodlor as he was too insignificant for Kil'jaeden to bother reviving. For the same reason, Aegwynn did not believe that the Burning Blade's activities were the result of Zmodlor acting on his own; as she put it, "a plan of this complexity is far beyond him". The identity of Zmodlor's master remained a mystery.