Gigantus was a massive planet (sometimes stated to be a Dyson Sphere) in the Gwydion System, in the Andromeda Galaxy, that dwarfed entire galaxies that existed millions of years ago.
It was home to the Gigantians a race of peaceful, technologically advanced people.
Their world was at peace until they were attacked by the Eternals of Eyung. The invasion went on for some time, but the Eternals soon could not handle the massive population and size of Gigantus and destroyed the planet.
The resulting destruction of the world of Gigantus spread debris across the universe, creating new stars, planets and moons, seemingly including the Sun, Earth and the Moon.