Primus is the creator-god of the Transformers. An ancient and ethereal being whose origins date back to the beginnings of the universe itself, Primus is a multiversal force for good, his life force existing across multiple realities and infinite alternate universes. In each one, he is the final defense against his fallen sibling, Unicron the Chaos-Bringer.
Primus's plan to contain Unicron's essence in the center of the sun failed when the star collapsed into a massive black hole (the Unicron Singularity) which threatened not only Cybertron and the universe, but the entire multiverse itself. The Autobots learn that the only way they can stop the black hole from consuming their home planet and the rest of the universe is to awaken Primus by inserting the four Cyber Planet Keys into the Omega Lock.

Related anime:

Transformers: Energon TV, 2004
Transformers Cybertron TV, 2005

Related manga:

Transformers: Kiss Players/15 Go! Go! Compilation Manga, 2005