George Washington hired his own Batman
Or rather, he had several of them under his command. In fact, long before Batman was a superhero, a "batman" was a military position. Officers in the U.S. and British armies had their own personal servants or assistants called batmen (or batwomen, if they were women). The batmen were also alternatively referred to as "orderlies" which kind of makes sense (Batman brings order to Gotham City!). Lord of the Rings author J.R.R. Tolkien even described the relationship between Frodo and Sam as being based on the officer-batman dynamic that he observed while serving in World War I in the British Army. Sadly, during the Revolutionary War, George Washington abandoned British slang and referred to his Batmen as "Orderlies" in his writings.
But why "batman" for a position that (usually) doesn't involve bats? In this case, "bat" is derived from the French "bât", a saddle put on horses and mules that lets them haul equipment around. (For Example). This gives the unfortunate impression that the real-life "batman" looked less like this and more like this.
These assistants lucked out with "batman", since it seems like they could have easily been "saddlebagger" or "donkeyboy" or "assman". Yes, somehow, an officer's servant gets a cool name like "Batman" but a naval captain who gets promoted is stuck with "Rear Admiral". There's no justice in the world!
Now that you know what a "batman" is, the 1967 hit British single "I Was Kaiser Bill's Batman" by Whistling Jack Smith finally makes sense!
Oh wait, it still doesn't? Sorry.
For more information on batmen, check out the Merriam Webster's dictionary definition, the Wikipedia article, and of course we recommend such historical texts as The Battery Commander, His Batman, and a Cook, A Biography of a Batman, and Braddock's Defeat; The Journal of Captain Robert Chomley's Batman. If you'd still like to learn more, I don't recommend trying to google it for yourselves. Searching for the military position and excluding the superhero from the results will end up looking like this.