Through oral history and independent research, I've found two main accounts of the origin of the King cake. First, however, some additional bits of info. The exact time during which they can be made and eaten is the Epiphany (January 6th) through Mardi Gras (varies). Doing so before or after will bring down the unholy wrath of anyone who's traditional about that sort of thing. The cake is usually made from long, thin strips of dough with a mixture of butter and brown sugar slathered on. They are then rolled up and sealed, forming long, round, rope-like strips of dough. These are braided together and formed into a ring. This is baked, and decorated first with icing, then with three varieties of colored sugar: purple, green, and yellow. These are also the official Mardi Gras colors, representing justice, faith, and power. The sugar is added in that same order, darkest to lightest, for aesthetic reasons. The purple will show up with yellow on it, but purple would drown out the yellow fairly well.

The first story is that a very long time ago, when France was known as Gaul, various tribes inhabited the area. To choose their leader, they would make a cake with a small nut or rock hidden in it. Whoever got this would serve as tribal leader (their king, basically) for a set amount of time, perhaps a year, and would then be killed.

The slightly more kid-friendly version, and the first I heard, was that in slightly more recent history, the French king would have a huge cake made with a small token in it. Whichever of his subjects got the piece with this unnamed token would then act as the king for a day. They, of course, weren't supposed to be killed at the end of their day.

In either case, it's fairly certain that the King cake originated in France, and was brought to America by French immigrants. This explains its popularity in areas such as New Orleans. The usual token for a King cake is a small plastic baby Jesus. They almost always look exactly the same, unless you give them plastic surgery with an over-enthusiastic bite. One final King cake tradition is for the person who finds the baby must bake the next one. This is not nearly as fun as being king for a day, obviously. So grab one of these treats and realize that despite all of this, they're far more stimulating for the stomach than the mind.