Among the many mysteries that a chronological watch of the Star Wars saga brings is the question of why Obi-Wan refers to Vader as “Darth” in Star Wars: Episode IV – A New Hope. Despite being the original Star Wars, A New Hope is chronologically the fourth movie in the saga, meaning that, theoretically, it should be in line with everything established in the prequel trilogy. Despite the 19 in-universe years that separate Star Wars: Episode III – Revenge of the Sith and A New Hope, the latter is supposed to work as a continuation of the stories of Obi-Wan Kenobi, Anakin Skywalker, and the Skywalker twins.
After Star Wars: Episode VII – Return of the Jedi concluded what is now known as the original trilogy, George Lucas decided to take the story back 30 years and show the early life of Anakin Skywalker. A sequel to the stories of Luke, Leia, and Han would then only be made in 2015, now under the Disney umbrella. Such an odd approach to the chronology of a franchise is bound to create canon inconsistencies such as Obi-Way saying “only a master of evil, Darth” when, in theory, the Jedi master knew very well that “Darth” was a Sith title and not the villain's first name.
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The real reason for it is that, at that time, “Darth” wasn’t supposed to be a title that would be used by other villains in the saga, but rather just a first name. Essentially, what the name “Darth” meant in Star Wars only had to do with the Darth Vader character himself and didn’t have any connections to any others. As the saga progressed and George Lucas introduced the concept of the Sith religion, the Star Wars creator brought the term Darth back, but now retconned as a title given
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