Kha-Beleth (also known as Demon Sovereign) is the main antagonist of Heroes of Might and Magic V and the undisputed leader of the Demon race in Ashan, who has ruled the jailworld of Sheogh since the disappearance of the Six Demon Overlords in 564 YSD. Enigmatic in his ways yet ineffably evil, his ambition to secure victory in the name of Urgash and resultant schemes define the events of Heroes V and, later, Dark Messiah of Might and Magic.
Rise to Power
Kha-Beleth rose to power shortly after the disappearance of the Six Demon Overlords; it is uncertain whether or not he played a part in their vanishing. In his early years at the helm of Sheogh, he began to preach "another possibility for demonic organization, [speaking] of a world where all Demons are created equal and have a right to live freely within and without Sheogh." He fought for the freedom of his people, but power twisted him.
When Kiril Griffin arrived to Sheogh, he sent Xana and Daeva to help in his tasks, as he was tricked by the Angel, Sarah. After he dealt with Sarah, Kiril begun to serve Kha-Beleth in his plans.
Gathering followers, he intended to use an impending Bloodmoon Eclipse to "gain a foothold on Ashan, and expose, if not impose, his people’s right to an equal place amongst the children of the Dragon Gods".
Queen Isabel's War
Due to his position as the Demon Sovereign, he was the commander of the demon forces during Queen Isabel's War. His top goal in this war was to impregnate Isabel Greyhound with the Dark Messiah. During the first stage of the war, he launched a raid-force consisted of Arch Devils to Talonguard, which interupted the wedding of Nicolai Griffin and Isabel Greyhound. Nicolai, fearing the safety of Isabel, told his uncle Godric to escort Isabel to the Summer Palace, while he battled the demons. Afterwards, Kha-Beleth launched a full-scale attack on the Holy Griffin Empire, which forced Nicolai to defend his empire. This was the perfect diversion for the Demon Sovereign to capture Isabel.
The Demon Sovereign tasked his agent, Agrael, whom had spied on her during her lifetime, to capture Isabel. Agrael then had his minion Biara kill Abess Beatrice and disguise herself like her. Biara, as Beatrice, persuaded Isabel to send Godric and herself to seek aid from the mages and the elves, while Isabel gathered the militia. Later, Biara as Beatrice returned to Isabel and told her that the elves would meet her. When Isabel arrived at the meeting-place, the Demon Lord Agrael ambushed and captured her. Agrael however, was in fact in love with Isabel, and offered her aid in escaping, but Isabel didn't trust the him and refused. Biara, whose loyalty laid with the Demon Sovereign, had overheard the conversation. Agrael then moved Isabel to Dunmoor and prepared her to transport to Sheogh, but she was freed by Godric.
After Agrael's failure, Kha-Beleth has learned of Agrael's intentions to kill him, thus becoming the new Demon Sovereign, and the fourth demon ruler through Biara. He sent the Demon Lord Erasial to kill Agrael and steal the Heart of the Griffin, an artifact capable of banishing demons to Sheogh. However, Agrael managed to capture Erasial, and intimidated him. Erasial gave the information to Agrael about the Heart, just before Kha-Beleth killed Erasial. As Biara got info from Agrael, Kha-Beleth then sent Veyer to capture the Heart of the Griffin, but Agrael managed to steal the artifact before Veyer, and banished Veyer back to Sheogh using the artifact.
Kha-Beleth learned that Isabel is going to Hall of Heroes to revive Nicolai, so he sent Veyer to take her. However, he did not plan that the Dark Elves, under Raelag's leadership, would foil his plans. He sent Biara to get the Heart of the Griffin from Tieru, to which she succeeded. Finally, Biara, disguised as Shadya, took Isabel so she could give birth to the Demon Messiah. However, Raelag, Godric, Findan and Zehir defeated Kha-Beleth, rescued Isabel and initiated the Rite of True nature on her.