Arcane Ordo Europae

Arcane Ordo Europae is an organization that is fairly hard to properly classify, as it straddles the fence between national agencies for supernatural defense and the international organization with its own agenda. AOE is one of the two main organizations responsible for paranormal security and law enforcement throughout the European continent. However, this makes it effectively larger than most national agencies, due to covering a small continent.
It is also one of the oldest continuously existing magical organizations, a fact that greatly adds to both its fame and infamy.

Structure

AOE is an organization that is to a certain degree upholding the aesthetic of the old aristocracy, although in much more lite version nowadays. It is a societal pyramid composed of a few thousand noble houses scattered throughout Europe, and assembled into a proper social pyramid with strong feudalistic undertones.
The highest ranked members of the Arcane Ordo Europae are the twenty eight royal houses, each of them led by a single individual that has received a title of a king, each of them overseeing (through their subsidiary houses) a significant territory. Most of those territories more or less equal that of a single country of the mundane world, however the borders aren't a perfect match, typically due to past events playing out a bit differently in the magic world.
AOE royalty of the past rarely felt the need to significantly alter their domains simply because of some (often temporary) changes to borders. It still caused a lot of local tensions in the past, especially during the period of time when Europe was divided between several large powers, such as the Austro-Hungarian Empire, with several magical kings clashing with each other over the title of de facto magical emperors of that particular part of Europe.
A number of those houses are directly tied to notable aristocratic of the mundane world - often down to carrying their name and considering themselves to be legal successors of those families. This happens to the houses that were born of the magical branches of those families that managed to leverage their family's mundane influence to elevate themselves to the position of the magical kings.
A fairly tame example of that can be the Habsburgs of Austria and Hungary, their house maintaining their power over core territories of their old empire, having effectively split off the real world Habsburgs completely. Much less tame is the case of the Merovingians of France - their overthrowing by the Carolingians being, in fact, caused by the last kings of the Merovingian dynasty dedicating themselves to worlds of magic while leaving the mundane world to the mayors of their house.
There are also cases of royal families that has never carried significant power in real world, managing to score big in the world of magic (or perhaps being born there entirely) and building off from there. It wasn't uncommon for those families to establish close ties with real world royalty of their domain, if only to expand its influence over the land while making sure that the families in question won't develop magical abilities. Here an example might be the Pendragons of England (with no discernible connection to king Arthur, who, for once, doesn't appear to be a myth connected to the magical world).
Beneath the kings, there are the dukes. The supportive network of heavily entranched magical families that form the backbone of every king's royal domain, each of them expected to offer more direct magical defense of regions they are responsible for, allowing the kings and queens to focus on larger threats. This is the lowest universally recognized noble title.
Beneath the dukes, there are either counts and barons (at least in the Western Europe) with a strict ladder of subservience, or simply noble houses with no hierarchy of titles (which tends to be a thing in the Eastern Europe).

Public Agenda

Arcane Ordo Europae's agenda is to maintain supernatural safety for the entirety of the European continent, while maintaining their own power and ensuring that no competitors to their power appear (all while doing their best to maintain the power of individual houses that make up for the AOE as a whole). In most cases, the former is given the priority.

History

Arcane Ordo Europae is an extremely old organization. While it's hard to say when exactly it was formed (as it was a process rather than something that was created through a singular decision), some expand its history all the way back to Carolingian Renaissance in the late 8th and early 9th Century. Although the name itself has been solidified properly in 18th Century.
It was initially formed as a secular occult division connected of the Erithian Catholic Church, formed out of the Church's decision to expand its power base by incorporating the smaller magical organizations (some of the dating back to times of the late Roman Empire) scattered throughout the Christian parts of Europe. Over time the organization has expanded in scope, for several centuries becoming the magical organization for Europe as a whole, while maintaining its ties with the Erithian Catholic Church.
It has eventually changed primarily due to Reformation, which coincided with a rise in pro-independence movement within the early AOE. This lead to weakening the ties between the Erithian Catholic Church and the Arcane Ordo Europae, although it has to be stated that those ties never vanished entirely. The AOE eventually became something of a magical high society of Europe, highly intertwined with aristocratic circles.
Unlike in case of the mundane world, among the initiates the aristocracy has mostly prevailed against the plutocracy and has never fully declined. The greatest attempt was performed by the magical circles adjacent to the freemasonry and the Iluminatii during the War of Enlightment, but even that has eventually failed.
From the perspective of the AOE's high society, the European Organization for Supernatural Defense is merely another attempt to hijack their prerogatives, leading to a sudden rise in tension throughout the European continent.