Pompus is the reigning king of Pumperdink.
A truth-telling golden mirror once described Pompus as a "Fat Old King." Pompus is somewhat authoritarian and mercurial, without being overtly evil or truly oppressive. He has a bad habit of sentencing his subjects to be dipped in a well for minor and trivial offenses; but the dipping is a relatively mild punishment.
Pompus also appears in the non-canon Oz novel The Blue Emperor of Oz.