I was thinking about the League of Extraordinary Gentlemen, and was wondering if there is some sort of equivalent in the Grimm Lands, fighting against injustices decreed by such figures as the Rotten King, the Queen of Hearts, and the Grand High Witch of the League of Witches and Warlocks. If so, what characters might be in it (ie Prospero, Caliban, Ariel, Hatter Madigan, Don Quixote, Natty Bumppo, Slue-Foot Sue, etc.)

I don't know who exactly they are or whether they even exist, but if they do, one thing is for sure: Red Little Riding Hood is their leader. There is no fairytale hero, in or out of the Grimm tales more famous then her.

I would say that the Cheshire Cat would be their spy-master - nobody notices a cat, in any case, and especially not one who can disappear at will...

I don't believe there are any written directly into cannon for the game. Grimm is set in a world where heroes are few and far between, which leaves the adventurers to fill that sort of role. My best suggestion would be another group of children, working towards the same goals as your party. This group may come head to head with the group when they both want a single item that will help them escape. Nothing better than pitting two groups of heroes against one another because they want the same thing. Grimm is a harsh land, I think the players should come to realize that even thier fairytale heroes can become bad. Not just that, but their characters themselves can see themselves in a rotten light.

Agreed. There is that ferret group, but there are no true heroes. Even Jack and Hansel and Gretel were corrupted. There are only small pockets, such as the original Bremen Musicians and Peter Pan.