[FatherDante]

Here's the real deal:

The retainer is a position in feudal european kingdoms, if every royal person dies, he retains the throne. Thence the name.

The Samurai serve under a general who serves undera daimyo which is an owner of a plot of land. The landowners are all governed by the shogun, who is the true leader. The Emporer was a symbolic figure, much like the royalty of modern England, he had little power.