We all know that the lion is often considered the King of Beasts, but how did this reputation arise? I can't say I know. Wikipedia just says that it's a consistent image of the animal, without really explaining the origin. I assume it has something to do with the fact that it's a powerful animal that looks noble, but I'm not sure what culture originally came up with the association between lions and royalty. Perhaps it's also due to how male lions living in prides usually let the females do the hunting and then feel entitled to as much of the meat as they want, which I'm sure many would say is an accurate representation of royalty. The lion was the symbol of the tribe of Judah, from which David and the other rulers of the Kingdom of Judah were descended, and I believe some translations even refer to the lion as king of beasts in Genesis 49:9. (The King James and New Revised Standard Bibles don't use this phrasing, but the Wikipedia article on lions says that the Tanakh from the Jewish Publication Society of America does.) The Egyptians had deities with the features of lions and lionesses, and Vishnu was also said to have taken a half-leonine form. Lions are, of course, also frequently found in heraldry and in statuary, often flanking the entrances to buildings.
In The Annotated Wizard of Oz, Michael Patrick Hearn has this to say on the subject of the lion as King of Beasts: "Although this belief goes back to ancient times and was prevalent in the Middle Ages, it was not until the Renaissance that it become [sic] part of a highly sophisticated system." He also mentions that works from the sixteenth and seventeenth centuries refer to the eagle as the king of birds, and the whale as the king of fish. Since a whale ISN'T a fish, though, I suppose that's sort of like when a country has a foreign king.
We'll see more on ruling lions on (most likely) Monday, when we take a look at a certain cowardly one.