He is the Sovereign giant in the Eternal Lands sky. His name was Zhou Fan
The Mortal Renegade killed his younger brother, and the woman they both loved. He wiped out the Immortal World, and then led his army of devilish specters on a path of extermination and destruction.
In the end, he killed all of the people in the starry sky, and destroyed all 180,000 worlds that existed within it. Just as he said, he cast the starry sky into complete darkness. And then, just as had been spoken of in the legends, the desolation and death caused the Eternal Flower to bloom.
According to such legends, the only way for a cultivator to break out of the Sovereign Realm was to use that Eternal Flower, and reach… the Eternal Realm!