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From the Encyclopedia Frobozzica:

Brogmoids - In rare cases, these squat creatures can achieve the intelligence level of a three-year-old human. Domesticated brogmoids are tame and can even be taught to perform simple tasks. In the wild, they can be seen in huge packs sorting through rock piles looking for edible rocks. From this fact it is not difficult to see why brogmoids live considerably longer in captivity.
The tenets of Brogmoidism, a religion originating in the fourth century GUE, state that a Great Brogmoid supports the world upon his shoulders, and that this Great Brogmoid keeps us from falling into the Great Void. Nowadays this belief is commonly ridiculed, and has lost most of its adherents, but nevertheless it is quite true. In 883 GUE the first Dungeon Master explored the depths of the Eastland's caverns and actually came out on the bottom of the earth to gaze upon a brogmoid that was tremendous beyond description. A rough estimate puts this Great Brogmoid at a zillion times larger than any brogmoid ever seen before. Its mere shoulder hairs were like mighty trees.
On the same day as this remarkable discovery, Curse Day 883, the first Dungeon Master also hiked to the top of Mount Foobia and discovered the foot of another Great Brogmoid. Apparently, not only does a brogmoid hold up the world, but upon the world is standing another brogmoid, which can only be presumed to support yet another world.
Chroniclers of history have always been puzzled by the fact that the Brogmoid Hypothesis has traditionally been given less credit than the so-called Turtle Theory, and the Troll Postulate, both of which were the subject of some research by Leonardo Flathead.