The most powerful individuals that represent the Fae as well as seemly empower them. Each court is it's own separate dimension that houses countless Fae and is under the full control of the monarch.
The rulers are known to have changed in the past, but it is a rare thing. Maybe once every few centuries and it's never an easy or smooth process as the entire court is affected by the power of their respective monarch.
Once one takes control of a domain, the Fae can't ever leave it unless they relinquish control. The four seasons seem linked in an never ending battle of influence as their influence is directly tied to the mortal world's climate. Each season wants total dominion over the others as it increase the powers of it's respective Fae.
If the Fae are ever threatened from the outside the monarchs will generally unite against the outsiders and push back. The powers they wield through their servants is a force to be reckoned with, as well as the ability to create portals at will which act as gateways between a court and any other dimension.