The Void
"We become aware of the void as we fill it."
The Void is aligned with neither Light nor Dark -- it is Nothingness itself. While Nobodies could very well be affiliated with the Void, there is no true master of the Void, and Organization XIII in particular, in wanting their Hearts back, are actually trying to fight against it in their own way. Even Enuo, the Warlock King, was ultimately swallowed up by the Void. The Void is Space, the Void is Nothingness, and the Void resides even in your own Heart. It is the quiet moment where you stop and consider your own mortality and, thinking of neither Hell nor Heaven, but ultimately that there's nothing hereafter, reward or torment. Few ever come to peace with the Void within themselves. The struggle to live, the struggle to be better, even the struggle for the fulfillment of selfishness all resist the call of the Void... but it is there in the Heart as much as any other element.
It usually, but not always, takes great suffering and despair for one to look towards the Void as a viable alternative to Darkness or Light. Sometimes it creeps up on someone as they lay awake at night, staring at the ceiling and thinking perhaps a little too much. It is said that when one looks into the abyss, the abyss looks back; something that is very true of the Void. Much like the other major cosmological elements that comprise the whole of creation, the Void is not inherently evil, but is instead anathema to much of what is considered “good.” Life, creation, and ethics -- all these concepts are meaningless to the Void and, indeed, one could say that the Void is often outright antagonistic to such concepts. However, with acceptance of the Void comes inspiration, understanding, and even peace. Without the Void, there would be no guiding drive to fill it. Without the Void, there would be no endings.
The Void has always been. There is no “Master” of the Void. The Void existed before creation. In the end, all returns to the Void -- and while that day may not come for untold millennia, it cannot be escaped.
There are some, though, who would have that day be tomorrow.
"Youth tries to fill the void, an old man learns to live with it."