Prime Nova

"We are Primus. We are Prima. We are Prime Nova. We are Sentinel Prime. We are Optimus Prime."

This unnamed Matrix bearer could be considered Prime Nova by process of elimination.

Prime Nova was the second Matrix bearer mentioned by the Creation Matrix. He presumably received it from Prima, and at the end of his watch he presumably passed it to Sentinel Prime.

Nothing is known of Prime Nova, his reign, or of its duration.

Footnotes

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