Character Analysis
Although Darth Vader remains the physical manifestation of pure evil, The Empire Strikes Back gives us a few glimpses of the human beneath that shiny black helmet.
Bad to the Mechanically Reconstructed Bone
Of course, he doesn't become all that human. Darth Vader is still the dude who will telepathically choke out his most prized admirals for making tactical errors, so make no mistake—he's still one bad Sith Lord. Also, his pursuit of the Rebels has become a relentless obsession, which we think has to do with a certain small town Skywalker from the rough streets of Tatooine.
There's no two ways about it—Vader is obsessed with hunting down the Rebels because of Luke:
VADER: If he could be turned, he would become a powerful ally.
EMPEROR: Yes, he would be a great asset. Can it be done?
VADER: He will join us or die, my master.
Although we don't realize this at the time, a repeat viewing of the film shows that Vader is clearly tortured by the knowledge of his son being alive, which drives his actions through the entire film.
After all, how else would you explain his refusal to kill Luke and suggestion of turning him to the dark side instead? Does Vader really want another power-hungry Sith Lord vying for his top dog status?
Dr. Jekyll and Darth Hyde
This is the emergence of Vader's human side. This is further emphasized on a symbolic level when we glimpse Vader in his meditation chamber, the only place where he can survive without his mask. We see the back of Vader's head briefly—it's pale white and pock-marked—before his helmet lowers and clicks into place. This establishes a conflict between Vader's technological and human sides that won't be concluded until the end of Return of the Jedi.
This is echoed by the conflict between Luke's image of his father and the reality of him as Darth Vader. Luke started his Jedi training in the first place because he had heard stories of his father's heroic exploits—exploits that, according to Obi-Wan, ended when Anakin was murdered by Darth Vader. Of course, he was murdered in a way—his former identity was blown to smithereens and replaced with that of the bad Mr. Vader.
Intergalactic Jerry Springer
Interestingly, Vader is still unwilling to kill Luke even when he has him on the end of his lightsaber. Just check out what he says:
VADER: Luke, you can destroy the Emperor. He has foreseen this. It is your destiny. Join me, and together we can rule the galaxy as father and son.
There are a few ways to read this statement. Is Vader just playing mind game to convince Luke to join the dark side, or would Vader actually prefer to be all evil-and-stuff with his son? While this point is debatable, it reinforces the idea that Vader does want to have a relationship with his son on some level.
The final moments of the film see Luke and Vader communicating telepathically: Luke doesn't even seem angry when he refers to Vader as "father," but sympathetic and caring. It's an odd moment. Whether you think that this is a signal that Luke is being tempted by the dark side, or that Vader is creeping closer to the light, you're going to have to check out Return of the Jedi to see the electrifying (literally) conclusion to Anakin Skywalker's descent into the dark side.
Darth Vader's Timeline