They all have one, but we often don't know what work they're from. The Ur-Example is the oldest known example of any given trope. "Ur-" is a German prefix meaning "proto-, primitive, or original" — that it is also the name of an ancient Sumerian city founded around the time that the earliest known writing systems were invented is serendipity.

Often, an Ur-Example doubles as the Trope Maker — but not always, and far less often with ancient tropes, which often evolved over a long period of time rather than suddenly bursting forth from someone's head, fully formed. When they're distinct, a Trope Maker differs from an Ur-Example in that the latter is realized to have met the definition of the trope only after later storytellers started doing it on purpose.

For instance, one of the pivotal Trope Makers of the Detective Story is Edgar Allan Poe's collection of C. Auguste Dupin stories; before Dupin, there is no story genre of fictional detectives going about the business of solving crimes. Nevertheless, while you may or may not know Poe's Dupin stories, you've probably encountered a certain Danish Prince named Hamlet,^Date: between 1599 and 1602 who not only sets about to ensnare his uncle King Claudius, but even incorporates into his plans a play-within-a-play he dubs "The Mousetrap". But half-a-millennium earlier still, "The Tale of the Three Apples" is a proto-Detective Story from The Book of One Thousand and One Nights ^Date: The earliest known extant copy of the Arabian Nights is a fragment that dates to the early 9th century CE, so, sometime in the early 800s — which would make "The Tale of the Three Apples" the Ur-Example of the Detective Story, or at least a possible candidate. But Wait, There's More! Oedipus Rex, first performed in 429 BCE, depicts Oedipus investigating the cause of the plague that has struck his realm. Which will give you an idea of the depth of the rabbit-hole a quest for the Ur-example can lead you down.^note Even more brain-twistingly, Oedipus Rex's mystery is also an example of The Killer in Me, which is generally seen as a twist on the expectations of the detective genre, despite appearing in one of the oldest recorded "detective stories"!

Wherever a trope has evolved gradually, determining the Ur-Example can be a complicated and contentious business. In many cases a trope has more than one Ur-Example, because determining the "earliest use of the trope" depends on subjective choices as to which aspects of the trope are its defining qualities.

This doesn't just apply to tropes, many times an idea is created by different people simultaneously or discovered and forgotten only to be rediscovered later. For example, who invented the telephone? Alexander Graham Bell, you might say. Wrong. Alexander Graham Bell and Elisha Gray both independently invented the telephone, but Bell got to the patent office first. Thomas Edison had the idea of wireless transmission of voice and signals but considered it unimportant, and it was forgotten until Marconi independently invented radio years later. And if this is the situation with something as concrete as an invention, imagine how easy it is with something as intangible as an idea for a concept in fiction.

Ur-Examples are unfortunately highly susceptible to the "Seinfeld" Is Unfunny trope — not only because they dreamed up conventions that have been around practically forever but both because, since at the time they were so new, the creators didn't really appreciate what they were making and thus didn't conform to the standards of an aesthetic or gimmick that hadn't even existed yet, and because (sometimes) they were trading on novelty value and suffer by comparison when we have alternatives to compare them to. See Unbuilt Trope and Beam Me Up, Scotty! for more on this.

Notable Ur-Examples: