Poetics

"A beginning is that which does not itself follow anything by causal necessity, but after which something naturally is or comes to be. An end, on the contrary, is that which itself naturally follows some other thing, either by necessity, or as a rule, but has nothing following it. A middle is that which follows something as some other thing follows it. A well constructed plot, therefore, must neither begin nor end at haphazard, but conform to these principles."

Aristotle may not have been the first troper, but he's the first troper for whom we have evidence, and the evidence is this work, Poetics, the great-grand-daddy of all Books on Trope.

It is based on his analyses of Greek epic poems, such as Homer's works, and of Greek tragedies, a term, which at the time, did not require an unhappy ending.

Full text here.

Tropes first described (to the best of our knowledge) in Aristotle's Poetics

 * Acceptable Breaks From Reality
 * Deus Ex Machina
 * Doing in the Wizard: Aristotle didn't approve; he preferred the aesthetically convincing to the merely possible.
 * Downer Ending: These endings he considered middle of the road -- better than some happy endings, worse than others.
 * Emotional Torque
 * Fatal Flaw
 * Happy Ending: Aristotle thought that the best plot for a tragedy was one in which The Reveal caused the hero to realize what he was about to do, and therefore not do it. On the other hand, he thought the worst was one where the character decided not to do an evil deed without The Reveal giving him a motive to do so.
 * Greek Chorus: Oddly enough, he just referred to it as the chorus.
 * Random Events Plot
 * Reality Is Unrealistic: Aristotle's opinion was that a story should prioritize being plausible to the audience over being actually realistic.
 * The Reveal
 * Special Effects Failure: Scenes that sound awesome in epic poetry can look ridiculous when performed on a stage.
 * Spectacle: Aristotle didn't approve much of it, either; he held that spectacle should only help a story tragic in itself.
 * Three Act Structure: Often cited as the earliest work to define it.
 * Tragic Hero
 * Unsympathetic Comedy Protagonist: He notes that comedies tend to portray people as worse than they are.
 * Wacky Wayside Tribe: Any part of the story that cannot be logically connected to the main action should be avoided.