The First Monarch was a title given to the ruler of the Sovereign Dynasty of Krios Prime, a government that was known on hundreds of planets in the mid-22nd century.
In 2153, the Kriosian Kaitaama rose to the position of First Monarch, several months after being kidnapped by a group of Retellians. She told Commander Charles Tucker III of the Starfleet ship Enterprise NX-01 to come visit her on Krios Prime after she had risen to the position, as she intended to issue several reforms concerning the courting of the First Monarch. (ENT: "Precious Cargo")