We'll spare you the elaborate academic theories on how the story is an allegory about politics and money. (Anyway, we think they seem a little far-fetched.)
But the Wizard of Oz himself could definitely be taken to symbolize crooked politicians. "Seeing me come from the clouds, [they] thought I was a great Wizard," he tells Dorothy. "Of course I let them think so, because they were afraid of me, and promised to do anything I wished them to do. Just to amuse myself, and keep the good people busy, I ordered them to build this City, and my Palace; they did it willingly and well" (15.70-15.71).
Wow. Selfish, much?
Hmm. So we have an unqualified leader who lies to the public to get what he wants. Once he's "in office," the Wizard continues this strategy, unconcerned with who he might hurt in the process. "When you came to me I was willing to promise anything if you would only do away with the other Witch," he tells Dorothy. "But, now that you have melted her, I am ashamed to say that I cannot keep my promises" (15.74). Once his scam is uncovered, the Wizard "resigns" from office, fleeing town in lieu of owning up to his mistakes. He never comes clean to the huge population that he has been so dishonest with, maintaining until the end that he is not a crook.