Komus

Komus, the Lord of Chaos, the Father of the Gods, Chaos Ascendant, is a primordial Warp Entity that is in fact not a Chaos God. While the Gods are born from mortal emotion and are single minded in nature, Komus' existence predates the mortal races, and perhaps even the Materium, as he has existed as long as the Warp itself has existed. Originally, he was the Warp itself, and omnipresent entity in the Immaterium. But after feeding off the emotions of newborn races, Komus unwittingly birthed the 4 Chaos Gods. They overthrew their predecessor, shattering him into billions of shards, including Furies and Enslavers. Since then, Komus has plotted his return. Any action in the name of Chaos Undivided gives him power. He has claimed the Black legion as his own, and marked Abaddon with the Mark of Chaos Ascendant, as a sign of the Despoiler's unknowing part in his scheme. Since Komus does not need the mortal races to survive, he cares not for eternal war, and instead seeks a final victory for Chaos. Essentially, he is Chaos in all it's forms.

He is omniversal, existing in both the Warhammer 40k universe and the Warhammer Fantasy Battles universe. His goal is the same in both: to destroy reality and usher in an age of Chaos in it's place. He first planned on using Be'Lakor to lead his Daemon Armies, but when the Gods undermined him, the Father of Gods turned to the mortal races, and chose champions to serve him. His greatest 2 Champions are Archaon and Abaddon, and so far only one has succeeded in his mission. Should Komus grow strong enough, he will rise up and consume all the Chaos Gods and regain his original position as Chaos itself. If this happens, all Daemonic entities will lose the mark of their respective God, replaced with the mark of Chaos Undivided, as a sign that their true master, Komus has returned.

Also, the Tyrant Star in Warhammer 40k is called Komus also because the star is a herald of his growing power.