As the Void itself has no actual physical form, residing between spaces outside this realm, it requires a messenger that will lead it's armies in a war against all of existence. Despite many of it's messengers falling in battle against the Warriors of Eternity, the Void never quits, and each new messenger is far deadlier and cunning than the one before it. As such, Omaltheron is not the one to be underestimated...
He spent many years as an undercover agent, travelling from world to world and spreading the seeds of chaos, unrest and anarchy among the masses, causing conflicts to spread across the universe and weakening the seal that keeps the Void from entering the realm. After spotting a weakness in the fabric of space, he tore it open, allowing his brethren and soldiers to pour in and attack. As a sort of counterpart to Valdora, he organizes the attacks of the Chaos forces and Void entities, sometimes leading the battles himself in order to confront the Warriors, and show them just how powerful he is. While he's more than capable of fighting toe-to-toe with each of them, and even causing them a lot of trouble, he has several weaknesses which they occasionally manage to exploit, forcing him to retreat into the shadows and rethink his strategies. As above mentioned, due to being Valdora's counterpart, he's completely fixiated on her, thinking of ways to mess with her head and make her suffer whenever he manages to get his hands on her. Despite being a brutal fighter and showing pleasure from bringing harm to others, he always maintains a calm and polite appearance, hardly ever raising the tone of his voice.

For some reason, I can't stop thinking about this theme playing during his debut: http://www.youtube.com/watch?v=Xy-Rd-M3MWk