The traditional options for the cohort would be Cleric or Wizard. But I'm going to suggest Archivist. Being an Int-focused character, he'd make a good advisor. But I feel like the Cleric spell list is more desirable from the perspective of keeping the province safe and prosperous. Plus, you can give him some choice non-Cleric spells, like Plant Growth, which lets him single handedly revolutionize the agriculture of the region.

Will the cohort also have the leadership feat?