Optimus Prime is an Autobot from One.
Bold and daring, Orion Pax came from humble beginnings as a cogless energon miner who, growing bored with his duties, snuck around in the archives to learn about the Primes. Yearning for adventure and the autonomy to make his own choices, he often tricked his by-the-books best friend D-16 into breaking the rules and getting them both in trouble.
Part of the reason for this is that the same relentless enthusiasm that drives Pax tends to blind him to potential flaws in his plans, such as their being dangerous. Or poorly thought out. Or just utterly stupid. And yet no matter how many setbacks he encounters Pax never loses faith that this time he's on to a winner, and it's that drive that convinces others to go along with him.
Despite this, his spark is very much in the right place, and as his sense of justice matured, he was bestowed the Matrix of Leadership, becoming the legendary hero Optimus Prime.