Prequels have a history that goes back almost as far as storytelling itself - and, one would assume, slightly before that, too. (Even Homer’s Iliad has a prequel, called Cypria, which was probably written in the late seventh century BC.) When we hear the word, though, we tend to think of the George Lucas definition. That is, to gracelessly explain previously unknown links in the narrative timeline that were probably best left unexplained.
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The Lucas Approach, we’ll call it, encourages creators to see prequels as an opportunity to counter criticisms of the original work by adding spurious backstory to flimsy plot elements: ‘Nuh-uh, it was supposed to seem ridiculous, because of this thing that happened before it that I only just wrote into the script now, so there’. For a fine example of this, see Rogue One, a $200 million dollar, 133-minute explanation of the Death Star’s faulty thermal exhaust port design.