Mage

A mage is one who uses arcane magic. Formally, the association of mages was founded and is currently headquartered in Hauntfall. The mage's college was a common place for northern nobles to send their children.
For centuries, the mage's association had something of a stranglehold on arcanism within the North- practically a religion unto itself, a headquarters building could be found within most cities. As a result of this mage solidarity, heavily reinforced by propaganda about larger threats than humans, most mages were reluctant to take to battlefields against each other. The prevalent elitism resulted in non-mages being considered fair game, especially due to the tendency for nobles to be the one getting the magical training.
While reluctant to fight other Northern kingdoms, mages did not hesitate to help repel invaders from the south (i.e. Terian Empire), whose anti-arcane sentiments clearly threatened their way of life. This was one of the key factors that facilitated united northern fronts in the case of attack from the outside.

Role

The magic of the northern regions is essentially a way to precisely exert physical force. This is primarily used in combat applications- some historians argue this as something of a cultural overreaction to the exodus from their original homeland, when their magic had primarily been used for construction.
The push towards high-speed casting and combat effectiveness meant that while the underlying principals hadn't heavily shifted from when the system of magic was used to manipulate stone, the lens through which they view these abilities has changed significantly.
Stone manipulation ended up being a forgotten art a few centuries after the great migration, despite it seemingly still being relevant with Sunstone manipulation. The culture's masonry actually heavily regressed as a result of this, unable to cold-weld fragments of stone as they previously could.
With the loss of earth manipulation, a mage can't really solve problems others can't.
Mages in the direct employ of kingdoms are generally just specialist troops. There are dedicated researchers in various academic instutions, Hauntfall employing the most by a significant margin (funded by alumni who are typically noble heirs themselves).