Here in South Louisiana in the weeks leading up to Mardi Gras we enjoy eating king cakes. The season begins on January 6, Epiphany, also known as Three Kings' Day (its eve is Twelfth Night, thus another name for them is Twelfth Night cakes). In the Christian tradition, this celebrates the revelation of the baby Jesus as Christ to the three wise men or kings. The European origins of this king cake tradition are explored in "Cakes for three Kings" found in the Gale General OneFile database. In Medieval times, a bean was often the hidden object representing the Christ child, and its finder was treated as "king" for the day. The article also compares the kings cakes and related confections from different countries and regions.
Stepping squarely into the recent past, "Sugared Babies" (accessed from EBSCOhost's MasterFILE Premier database) discusses the importance of New Orleans's McKenzie's bakery in making the king cake as widely popular as it has become since the mid 20th century, in part by innovating the plastic baby which has become the standard "find" in the New Orleans traditional king cakes. For a look at some creative savory takes on this cake, see "A Retreat from Sweet" (Times-Picayune, from the Newsbank database). Finally, the cookbook New Orleans Classic Celebrations, by Kit Wohl, includes a recipe for traditional New Orleans king cake.
As a little lagniappe, for an interesting exploration of a tangentially related custom, see Ribbon Pulls in Wedding Cakes: Tracing a New Orleans Tradition.