The Old Gods were an ancient race in the DC Universe.
Around 18 billion years ago, the Old Gods originated from GodWorld (also known as Asgard). After 10 billion years of a golden age, an evil called Ragnarok came that saw GodWorld being torn asunder in a great explosion called the Godwave where the gods perished. The energy unleashed seeded worlds with the potential to eventually bring forth gods of their own. Such a world was Earth.
About 4.8 billion years ago, the remnants of GodWorld would eventually create two separate planets: Apokolips and New Genesis. New Genesis became dedicated to peace and goodness. Apokolips developed into a cruel, warlike culture. Thus rose the New Gods as the planets warred.
Some of the Old Gods had survived their racial extinction, for example the Dreggs (who live below the surface of Apokolips), Arzaz and the Nameless One.