Optimus Prime was the last born of the original Thirteen Transformers. Her spark was the most like their progenitor Primus, its frequency nearly identical. She was the mediator and visionary of the group, passing among them all as a calm, inspiring, thoughtful, unifying and well-liked friend. It was her unique spark and her inspiring reassurance that "All are One" that allowed the Primes to rally and succeed in their battle against the Chaos Bringer Unicron. When tragedy at last ended the era of the Primes and brought forth the new race of lesser descendant Transformers, her alone chose to be reborn in the Well of All Sparks as one of them, that he might know them and their needs more completely