Follower

Followers are especially loyal low level characters who can be attracted by the Leadership feat. Despite their low level of power, their loyalty can make them very valuable in duties that are reasonably safe, but require absolute loyalty; such as guarding or handling secret documents, carrying confidential messages, preparing your food, making your bed, and otherwise being loyal staff.

Followers do not earn experience.

If one imagines a cohort to be one's squire, then followers can be understood as heralds, grooms, minstrels, and pages, becoming the character’s entourage.

Variant
Since a Birthright campaign, unlike a normal D&D campaign, is overflowing with 1st level warriors, and not every player is excited to receive a kitchen servant too loyal to allow poison into their master's dinner; there is some cause to allow followers to gain experience. Based on a normal campaign where the most powerful human regents are 9th to 12th level, allowing followers to climb to 3rd and 4th level would probably be justified. Typical classes being expert, warrior or rogue.