Yes, I know he was only 6 feet, and yes I know Darth Vader is 6'6 but couldn't that just be his suit? Maybe Skywalker lost his legs in the attempt on his life?
Just fishy that he disappeared and then like a month later the Emperor introduced us to Darth Vader.
While dubious by historical standards, Luke Skywalker claims to be the son of Anakin Skywalker and was told this by several Jedi. He futher claims that Darth Vader told him that he was Luke's father but due to a lack of medical documentation, documentation of his mother, and any real proof to tie Darth Vader with Anakin Skywalker, it is hard to substantiate such a claim.
Further, it would be very hard to believe that the hero that was Anakin Skywalker would fall to the darkside despite fighting so hard against Count Dooku.