A lion, a fox, and a wolf went hunting one day and brought down a fine stag. The lion carefully divide it into three equal parts and when this was done, said "Now, as king of the beasts, I will take this part, and for my role in the hunt, I will take this part. As for the third part...who wants it?"
And thus it is said: Caveat socius.
Notes
There are two stories (at least) in Aesop that have the lion and other animals hunting. The first gives rise to the phrase "lion's share" and is (I suspect) far better known as it makes the unfairness of the division quite clear. I prefer this version, as it's a lot more subtle (insofar as it can be).