Just logged in to respond to Joe's comment: The sheik is especially popular in romance novels because he's the closest thing to a prince. He's rich and aristocratic and powerful, and the princess fantasy of the stereotypical knight on the white horse is why the Disneyfied fairy tales are popular.

And there are two ideas of a sheik. One is the horseman, the wild "barbaric" raider living in a tent, and the other one is the rich guy with a palace who often has ultiple wives.