The One

The One is Unicron and Primus's daddy.

The One is the central nexus of all forces in the Universe and the source of Chaos and Order. The One is not necessarily a Transformer, or even necessarily a robot, but he created the multiverse, and that's pretty awesome by itself.

Also they seem to have some connection with the Vok, as shown in Primeval Dawn Part Three.

From Teletraan I: The Transformers Wiki, a Wikia wiki.