8 Ways Darth Vader Almost Turned Out Completely Different
2. He Wasn't Lukes Father Until The Second Draft Of Empire
Darth Vader is allegedly Dutch for dark father (it's not actually - dark is donker). But don't let that fool you into thinking Lucas had that whopping, universe-altering twist planned all along; he fact that Darth Vader is actually Anakin Skywalker, Luke's father, wasn't dreamt up until the second draft of The Empire Strikes Back.
Looking at earlier versions of A New Hope it's obviously made up on the fly; Annikin Skywalker (née Starkiller) and Vader are two distinct characters in all drafts of the first film, while when you ignore the sloppy retconning ("from a certain point of view") even the finished movie points away from it. There were even scenes shot for the first Star Wars that, had they been included, would've made no sense; the scene of Red Leader talking to Luke added into the Special Editions originally had some discussion of his father cut.
When that idea was created suddenly there were two Star Wars timelines; the one where Vader kills Anakin and the one where Vader is Anakin. The former, alternate saga would have been a wildly different beast, with the story of Luke less emotionally wrought and more typical, while Vader would be far from the three dimensional villain he became. It's this timeline where the previously mentioned of killing off Vader came from.