But his character started to lose a lot of credibility after The Empire Strikes Back...
From A New Hope
"If this is a consular ship, where is the ambassador?!"
In this early scene, Vader shows his superhuman strength by easily holding up Captain Antilles by the throat with one hand.
"I find your lack of faith disturbing."
In this memorable moment, he casually Force Chokes an Imperial soldier just for talking back to Vader by simply pinching his fingers together.
"I've been waiting for you, Obi-Wan. We meet again, at last. The circle is now complete. When I left you, I was but the learner. Now I am the master."
Here, Vader just stood there as if Obi-wan played right into his hands. You can almost hear Obi-wan mutter "oh crap!" under his breath.
"Your powers are weak, old man."
This quote was shortly before Vader delivered the death blow to Obi-wan.
From The Empire Strikes Back
"You have failed me for the last time, Admiral."
These were the last words an Imperial Admiral heard before being Force Choked to death because he inadvertently came out of lightspeed to close to the Hoth system.
"Apology accepted, Captain Needa."
This was Vader's response to Captain Needa's apology for losing the Millenium Falcon. Oh, and Vader also Force Choked him to death.
"We would be honored if you would join us."
Lando betrayed Han by bringing him before Vader. Han shot at Vader with his blaster. Vader simply held up his hand to deflect the shot and Force Pulled the blaster from Han. Pwned.
"Perhaps you think you're being treated unfairly?"
This was Vader's response after Lando suggested that they had never agreed to hand over Han to Boba Fett.
"I am altering the deal. Pray I don't alter it any further."
Vader had previously agreed to let Leia and Chewie stay in Bespin but he subsequently ordered Lando to hand them over to him. Lando is just being toyed with the whole time.
"The Force is with you, young Skywalker, but you are not a Jedi yet."
Here, Vader taunts Luke prior to their first duel, suggesting that Luke is simply just not good enough to beat him.
"You are beaten. It is useless to resist. Don't let yourself be destroyed as Obi-Wan did."
As Vader predicted, he severs Luke's hand and defeats him.
From The Return of the Jedi
"I hope so, Commander, for your sake. The Emperor is not as forgiving as I am."
Vader is angry at the slow construction progress of the 2nd Death Star. Upon learning that the Emperor will be paying a visit, the Commander suggested that they will double their efforts.
From The Empire Strikes Back
"What is thy bidding, my master?"
So all this time, Vader was just a pet under the control of Palpatine?!
From Return of the Jedi
"Obi-Wan once thought as you do. You don't know the power of the dark side! I must obey my master."
Again, this just confirms that he's a slave.
"It is... too late for me, son. The Emperor will show you the true nature of the Force. He is your master now."
This was kind of like Vader admitting impotence to his own son.
"You already have, Luke. You were right. You were right about me... Tell your sister... you were right..."
Talk about letting all the air out. This had to be the most disappointing moment in the Star Wars saga. We finally get to see the man behind the mask and he's just an fat, old, bald dude.
From The Phantom Menace
"I can't do it, Mom. I just can't do it."
9-year old Anakin was just a momma's boy...
"Are you an angel?"
Actually, every line uttered by Jake Lloyd as 9-year old Anakin Skywalker just tarnishes more of Vader's legacy.
From The Attack of the Clones
"So have you. Grown more beautiful, I mean. Well, for a Senator I mean."
Smooth talker, eh?
"Attachment is forbidden. Possession is forbidden. Compassion, which I would define as unconditional love, is essential to a Jedi's life. So you might say, that we are encouraged to love."
"Excuse me, I'm in charge of security here, milady."
Anakin tries, unsuccessfully, to wrestle control of the situation from his future wife, Padme.
"I don't like sand. It's coarse and rough and irritating and it gets everywhere. Not like here. Here everything is soft and smooth."
The all powerful Lord Vader has a soft spot...
"From the moment I met you, all those years ago, not a day has gone by when I haven't thought of you. And now that I'm with you again... I'm in agony. The closer I get to you, the worse it gets. The thought of not being with you- I can't breath. I'm haunted by the kiss that you should never have given me. My heart is beating... hoping that kiss will not become a scar. You are in my very soul, tormenting me... what can I do?- I will do anything you ask."
I feel sorry for Padme. This has to be the most uncomfortably awkward moment ever...
"You're going to pay for all the Jedi that you've killed today, Dooku."
Unfortunately, Anakin just doesn't have the skills to back up his words and loses his arm in the process.
From The Revenge of the Sith
"You are so... beautiful."
Another smooth line by our powerful Dark Lord of the Sith...
"What? How can you do this? This is outrageous, it's unfair."
What a brat...
"I will do whatever you ask. Just help me save Padme's life. I can't live without her."
Ok. There are two wars going on. One is between the Republic and the Seperatists and the second is between the Jedi and the Sith. Anakin is a Jedi Knight serving the Republic. He decides to prioritize his dream of his wife dying ahead of these 2 wars? That's a bit iffy isn't it?
"You underestimate my power!"
Apparently, Obi-wan knew exactly how capable Anakin was. Immediately after this line, he completely sliced up Anakin's limbs.
"Where is Padmé? Is she safe? Is she alright?"
It's just very odd hearing Vader say this with his mechanical voice...
Of course, how can I leave out the most memorable line of the movie. Like father, like son.
From The Force Unleashed
"I've trained you well, but you still have much to learn."
Vader was wrong as he gets completely owned by Galen Marek. His helmet gets sliced off and suit is all busted up.
From The Force Unleashed 2
"As long as she lives, I will always control you."
Let's recap. A couple of years ago, Vader lost to Galen Marek in all aspects of battle. It was obvious that Galen was superior in both lightsaber combat and in Force abilities. Now, Vader loses to Galen again (albeit a clone). Galen is holding Vader as captive. Considering the circumstances, Vader's words just don't really hold up.