The point is, the sequel/remake machine seems to be a phenomenon of the last 30 years or so; after all, we never saw a Casablanca 2: The End of a Beautiful Friendship.
It Actually Started: In 460 B.C.E.
To find the beginning of this kind of creatively bankrupt money grab, you need to go way back, before the patch of land we know as Hollywood featured so much as an adobe hut.
One of the oldest existing works of Western literature, Homer's The Iliad, has a slew of sequels attached to it -- playwrights like Sophocles, Aeschylus and Euripides each cranked out stage performances about the days and years after story of The Iliad, following the heroes' exploits after the Trojan War. Hell, one of the sequels, The Oresteia, spawned its own franchise that itself got multiple sequels.
Via Wikimedia Commons
Don't worry, buddy -- we had the same reaction when we heard about Fast and Furious 5.
That's right: All the way back in biblical times, mankind had already invented goddamned spinoffs.
But if we want to talk about beating a series to death, let's look at the king of Western literature himself, William Shakespeare. The man was the Sylvester Stallone of playwrights, pounding out no fewer than seven plays chronicling the stories of the various King Henrys throughout history. The immortal bard eloquently labeled them: Henry IV Part 1, Henry IV Part 2, Henry V, Henry VI Part 1, Henry VI Part 2, Henry VI Part 3 and Henry VIII: The Henryocalypse. There would have likely been many more, and probably a gritty reboot, if the theater hadn't burned to the ground after a fire started during a performance of Henry VIII.
After that, all of his explosion scenes were done with CGI.