Like the phrase "peeping tom" is used to refer to a creep trying to see somebody else using the bathroom. What on Earth did this Tom character do to become the definition of such a creep?
Why are women who do not have traditionally feminine traits sometimes called tomboys? Why Tom?
And why do people say "Bob's your uncle"? Was this Bob a super helpful and reliable guy, so much so that his name is used for the definition of something being finished and done?
And the playing card representing an aristocratic / upper class man is called Jack, who is this Jack? Why do people say a "jack of all trades", was this Jack character incredibly talented? Or is it related to the playing card, where they are good at everything but not the best (i.e. a king or queen)
I know of a few that are of religious origin, like the Achilles's heel after Greek mythology, and the bumpy bit of your throat is called Adam's apple is biblical.
Peeping Tom is a character from the legend of Lady Godiva (real Lady, probably made up story). Basically Lord Godiva was an asshole / tyrant and Lady Godiva begged him to have mercy on her subjects.
He was all "well if you like them all so damn much go ride a horse naked across the whole land so they can all see yo hoeass"
and she was like "OK then you'll stop being an asshole? Bet."
and he was all like "do it then bitch."
So she fuckin' did and all the subjects averted their eyes and/or stayed indoors except some weirdo named Thomas who was subsequently struck blind or dead by some angels or some shit.