Malreppidar
Malreppidar, based in the Core of the Milky Way, controlled not only every known galaxy in our universe, but also a vast majority of those in the Secondary Spaces.
Malreppidar may have ruled over septillions of creatures.
After the fall of Avethell, the Gergathan proclaimed Malreppidar, and began the systematic destruction of all life in other galaxies. Before this effort was really begun, about 3 million BCE, intercontinuual travel was developed, and Malreppidar spread like a virulent plague into the Secondary Spaces. (The Deserted Worlds of the New Continuum date from this era.)
About 2.7 million BCE, a tributary state in an adjacent continuum revolted and seriously damaged the Gergathan. Malreppidar fell.
The Kohlenebian Empire carried on the Core culture in the Scattered Worlds, but a true successor to Malreppidar did not appear until about 900,000 BCE, with Kaypleskrit.