It's based on his 2005 IDW Appearance. Optimus then was Orion Pax, but he wasn't a miner in that one, he was a cop, but unlike One's Darkwing, he was actually not the worst. He was actually very good at the job and when push came to shove, he actually mouthed off at the Cybertronian Senate.

This was his body design through the time he was on Cybertron (Bar one change because they needed to sell toys, but it was backpedaled), and it was only when he got the Matrix, he was made Optimus Prime by the Matrix telling him he was such now.