I just came across this question, and it was closed as "off-topic". It appears from the comments that it was closed essentially as General Reference or Too Trivial, both of which I thought had been burniated.
It does seem like a simple question, but if it wasn't obvious to the asker (and it is clearly a sci-fi...err science fantasy question), then it probably was not obvious to others. I can see a detailed answer, probably with spoilers, detailing Vader's turn to the darkside and then Luke's influence on turning him back. Probably not worthy of a Great Answer badge, but a solid answer nonetheless.
So why was this closed?