I'm about 30% through book 3 now, god damn. God. Damn. I'll be able to read all your spoilers soon, you bastards.
Also, I landed on the Wikipedia page for "Usurper" and it ended with this:
"Some famous examples considered usurpers are Pope Leo IX, George W Bush, Henry IV of England, Catherine II of Russia, Miguel of Portugal, Robert Baratheon of Westeros, Habibullah Ghazi of Afghanistan."