Druids (in 2e)

I touched previously on how the Cleric class (and by extension the Druid) is the one who's presentation does the most to set parameters on the fantasy world.  I think a special mention must be made for the Druid class for AD&D 2nd Edition.

• The Text of the Druid Class explicitly states they have a world wide structure.  
• Some "thing" even prevents them from leveling up past 12th level unless they interact with this world wide organization.  Typically needing to defeat another Druid of the given level.  
• There is a Grand Druid of 15th level who oversees the world.  This Grand Druid has a "staff" of Druids who serve as messengers and they gain additional spells slots. 
•  Beyond 15th level, they join the ranks of super druids whose bodies do not age, can alter their appearance at will, hibernate for ages, and travel to/survive the elemental planes.  

Combined with their standard ability to take on animal form and secret language, this is a world altering cabal.  Any animal could be a Druid in disguise or their agent.  Heirophants can impersonate high ranking folks.  They can see their agenda across human lifetimes and coordinate across the world and other planes.

Now, I love this bit of lore, and always keep it in mind for my games.  However, flavorful as it is, it does not fit into my default D&D world.  First, the Druid is not a part of all editions, and this lore specifically does not really appear anywhere else.  Finally, it is very specific and locks in certain other conventions that I would rather leave vague until needed.

On the other other hand, some interesting things to consider.

• No mention of Gods.  Those Druids who say they worship a nature deity are either mistaken, or going along with the cover story in order to avoid persecution by "the church".
• Grand Druids have extra spell slots.  So whatever grants their power, formally recognizes the stucture of the Druid order and its politics.
• Grand Druids have their own staff of lower level druids who are outside the hierarchy and level restrictions.  So whatever mechanism prohibits leveling up for Druids also recognizes the hierarchy and political station of the Grand Druid's staff.
• The Druidic language is secret, but known by all Druids.  It is not known by sylvan, elemental, or other allied beings.  It is something developed and used exclusively for the sake of the hierarchy.

So in short, the 2e Druid class has mechanics that define, inform, imply the most about the workings of the game world than any other class in D&D.