Promachos is a temporary position during wartime in which a member of the Chromeria government is appointed to rule absolutely.
During the War Of The Prisms, Gavin Guile was appointed Promachos. With the advent of the Colour Prince's insurrection, Andross Guile, father of Gavin and the Red of of Spectrum, was appointed to the position.
It is not clear what the requirements are to be eligible to become Promachos. Of the two known examples, one was Prism and the other was a member of the Spectrum, but it is possible, though unconfirmed, that the White, the Black, the commander of the Blackguards, a Satrap, or even any sufficiently-qualified person could be named to the position.
Notes:
The practice of Promachos is based on the practice of Dictator from the ancient Roman Republic. Normally, the Republic was ruled jointly by two Consuls. However, during war or emergency, a dictator could be appointed to lead the republic until the crisis abated (normally six months, unless the Roman Senate approved a motion to extend the Dictator's tenure. They could also name a new Dictator at the end of the previous one's term of service.) This practice led to problems when Dictators refused to give up their positions at the appointed time. A notable example of the system working correctly was in the case of Lucius Quinctius Cincinnatus, a retired solider and politician who came out of retirement to serve as Dictator when the Republic was invaded by a barbarian tribe known as the Aequi, then relinquished his position as soon as the threat was dealt with and he was no longer needed, and returned to his farm.