Alec Guinness: Ben 'Obi-Wan' Kenobi
Luke Skywalker : [approaching R2-D2] I can't do it, R2. I can't go on alone.
Obi-Wan : [from out of sight] Yoda and I will always be with you.
Luke Skywalker : Obi-Wan.
[Obi-Wan's spirit approaches Luke]
Luke Skywalker : Ben! Why didn't you tell me? You told me that Darth Vader betrayed and murdered my father.
Obi-Wan : Your father... was seduced by the Dark Side of the Force. He ceased to be the Jedi Anakin Skywalker and "became" the Sith Darth Vader. When that happened, the good man who was your father was destroyed. So, what I told you was true... from a certain point of view.
Luke Skywalker : A certain point of view?
Obi-Wan : Luke, you're going to find that many of the truths we cling to depend greatly on our own point of view. Anakin was a good friend. When I first met him, your father was already a great pilot. But I was amazed how strongly the Force was with him. I took it upon myself to train him as a Jedi. I thought that I could instruct him just as well as Yoda. I was wrong.
Luke Skywalker : There is still good in him.
Obi-Wan : He's more machine now than man. Twisted and evil.
Luke Skywalker : I can't do it, Ben.
Obi-Wan : You cannot escape your destiny. You must face Darth Vader again.
Luke Skywalker : I can't kill my own father.
Obi-Wan : Then the Emperor has already won. You were our only hope.
Luke Skywalker : Yoda spoke of another.
Obi-Wan : The other he spoke of is your twin sister.
Luke Skywalker : But I have no sister.
Obi-Wan : Hmm. To protect you both from the Emperor, you were hidden from your father when you were born. The Emperor knew, as I did, if Anakin were to have any offspring, they would be a threat to him. That is the reason why your sister remains safely anonymous.
Luke Skywalker : Leia! Leia is my sister.
Obi-Wan : Your insight serves you well. Bury your feelings deep down, Luke. They do you credit, but they could be made to serve the Emperor.