The original title of Return of Jedi was Revenge of the Jedi, and here's why: It's the third movie in what was, at the time, a trilogy. Of course, we now know that it's the sixth in a series of nine movies—that's called an ennealogy—but back in 1983, Revenge of the Jedi was poised to tie up all of the loose ends in the Star Wars saga, and bring the whole shebang to a satisfying conclusion: The Jedi return, led by Luke, and they finally get their tasty revenge over the evil Empire.
Why'd they'd change the title, then? Because, according to screenwriter George Lucas, the concept of revenge isn't very Jedi-like. Revenge became Return, and everything was hunky-dory. Well, except for the fact that promotional materials like posters—and even a teaser trailer—with the Revenge of the Jedi name had already been produced. Whoops!
In the end, the Revenge of the Jedi trailer is preserved online, and those posters were happily scooped up by Star Wars fans. Today, they're super-cool collectors items.
Don't worry: Lucas got to plug the concept of revenge back into his ennealogy with Star Wars Episode III: Revenge of the Sith. The Jedi may not be cool with revenge, but the Sith? They love the smell of vengeance in the morning.