Primus

Primus, also known as The One and Prime and the Supreme Modron, was a Greater Power and the immortal ruler of Mechanus and the modrons. Primus is said to be perfectly ordered and forever fair. While it retained godlike power within its realm, Primus was not immortal and could be killed. Like all gaps, that vacancy is immediately filled by promotion of a secundus. That creature immediately gains the powers of the old Primus. It usually takes a bit of time for the new Primus to determine the state of the planes and of Regulus and decide what needs to be done.