The first Return of the Jedi poster had the wrong title. The title is one of the first things audiences learn about new Star Wars movies, but in this case, it was changed in a pretty major way.
When George Lucas announced what was then the third Star Wars movie, the title was given as Revenge of the Jedi. This was pushed heavily in a striking poster with predominately black and red coloring. Of course, then it all changed. In December 1982, Lucas changed the title just five months ahead of its May 25, 1983 release date to the Return of the Jedi that we all know. This despite merchandise, posters, and even a teaser trailer all featuring the "Revenge of the Jedi" title.
To this day, the exact reason behind George Lucas's motivation to change the title is contested. Common lore says Lucas wanted to soften the title because Jedi are not trained to seek revenge and so he wanted a title that was more reflective of Jedi values. It's also been alleged that Return of the Jedi had always been Lucas's original, intended title, with "Revenge" only used to curb fake merchandise. It's also been suggested that the move was made to avoid conflict with 1982's Star Trek: The Vengeance of Khan (later changed to Wrath).
While fans don't give Return of the Jedi a second thought today, not all involved were happy with the change at the time. The film's screenwriter, Lawrence Kasdan, reportedly argued the word "return" was too weak. And, to his credit, the "Revenge" title does make sense.
Coming off the back of The Empire Strikes Back, it would signal the direction Luke Skywalker's journey is going in. Intent on bringing his father back from the Dark Side, Luke was dealing with a lot of heavy emotions, with the movie meant to play with his morality a lot more than is often accepted. As a Jedi-in-training with a big chip on his shoulder, describing Luke as a man prone to revenge feels rather apt. The change shifts focus onto Darth Vader, with it now describing (and spoiling) Anakin Skywalker's redemption.
Even though the word "revenge" didn't stick in the Episode VI title, Lucas did find a way to get the word back into the Star Wars saga: on May 19, 2005, Star Wars: Episode III - Revenge of the Sith was released in theaters.
