Mediator

The Mediator is a sentient piece of software that resides in the Matrix of Leadership, greeting its new bearers and presenting them with the choice to claim or reject the mantle of a Prime.

Fiction

2019 IDW continuity

When the Matrix of Leadership reacted to Orion Pax following the death of Sentinel Prime, the Mediator greeted him in the likeness of his mentor Codexa, telling him of the Matrix's history and what was to come. After the orientation, the Mediator offered Pax the chance to reject the burden but he accepted it and was reformatted into Optimus Prime. Prime

The Mediator later summoned Optimus back into the Matrix to warn him that Cybertron was preparing to die, spreading its fear to all its inhabitants, and that Optimus had to retain his optimism if he was to unify and save the planet. Radical Time