Zmodlor

Zmodlor is a minor demon who specializes in infiltration. During the events in Cycle of Hatred he recruits citizens of Orgrimmar and Theramore into the Burning Blade and uses them to raise tensions between the orcs and humans. He was banished thanks to the combined efforts of Aegwynn and Jaina Proudmoore.

Confrontation with Aegwynn
Centuries before the opening of the Dark Portal, Zmodlor took over an entire schoolhouse full of children in the village of Jortas. Zmodlor was preparing to perform a ritual that would have poisoned the souls of the children when the Guardian Aegwynn discovered his activities and banished him back to the Twisting Nether.

Zmodlor's return
During the Third War, Zmodlor was among the demons summoned to Azeroth. One of many demons who survived the war, Zmodlor sought to destroy the fragile peace between Orgrimmar and Theramore.

Zmodlor recruited both orcs and humans who were prejudiced against one another into a new incarnation of the Burning Blade cult, promising each that he was only interested in helping them destroy the other. None of his minions were aware that he was also recruiting among their enemies. Among the members of Zmodlor's Burning Blade were Jaina Proudmoore's chamberlain, Kristoff, and Burx, one of Thrall's chief warriors. Another was the human Margoz, who recruited new members in the Demonsbane Inn in Theramore. When the soldier Strov followed Margoz from the inn to investigate, Zmodlor slew him. Zmodlor later cast protective wards to trap Jaina and Aegwynn in Bladescar to prevent them from interfering.

Zmodlor's plan nearly succeeded, and a battle had already broken out at Northwatch Hold before Jaina was able to discover Zmodlor's hideout atop Dreadmist Peak. Jaina and Aegwynn confronted Zmodlor and several of his warlocks, where they were able to banish him to the Twisting Nether yet again.

Aegwynn did not believe that Zmodlor was acting on his own in using the Burning Blade to inflame violence between Orgrimmar and Theramore, telling Jaina that "a plan of this complexity is far beyond him". The identity of Zmodlor's master remained a mystery.

While speaking with Thrall following these events, Jaina stated that the Burning Legion would have a hard time rescuing Zmodlor a second time and that because he is a minor demon it would not be worth the effort.

Zmodlor's master
Though it was never hinted beyond Zmodlor's master being smarter, it is reasonable to assume that the Shadow Council in Felwood was ultimately responsible for the plan because the Burning Blade is part of the Shadow Council.

Zmodlor's race
Cycles of Hatred never specifically states what kind of demon Zmodlor is, but he is described as a huge demon with leathery skin, bat wings, and flaming eyes.

Nathrezim, doomguards, and annihilan all fit this description, though nathrezim and annihilan are rarely described as "minor" demons as Zmodlor is. Zmodlor's work also involved a lot of subterfuge, which is generally considered to be the specialty of the nathrezim, but Aegwynn did state that he did not have the intelligence to come up with the scheme on his own.