Why did anakin skywalker become Darth Vader?

Why did anakin skywalker become Darth Vader?
we think darth vader is that big ugly guy in the black costume? well thats half true.
darth vader decided to join the dark side of the force because chancellor palpatine convinced him the jedi are evil. he also made anikan change his name into darth vader as he said, " henforth, you shall be known as Darth Vader." he went and tried to kill Obi Wan kenobi, but failed and obi won cut his limbs and he fell into lava. palpatine found him and gave him a robot suit so he could survive.

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I don't wish to edit the first answer. It answers the question of HOW did Anakin Skywalker become Darth Vader, but not really why. It is not clear to me why Anakin gave up hope and signed on with Palpatine (or Darth Sidious). Was he manipulated mentally by Palpatine? Was he just stupid? I mean he had all this Jedi training and had done so much good, why throw it all away, even if he felt he'd blamed for the death of Mace Windu? I mean it's understandable that his role in Mace Windu's death (he cut off Windu's hand as Windu was about kill Palpatine/Siduous, and then Sidious turned on Windu) could cause him grief. But then. right then, he submitted to Sidious right away knowing fully well he had been manipulated by him all along. Why trust a manipulator?

Later comic books and novels have explored why he did give into the dark side a bit. Let's assume he was SO confused by Windu's death that in a moment of weakness gave into Palpatine/Sidious believing Sidious could save Padme's life. Yet he goes on and fights Kenobi and kills all the Jedi children and goes after all the Jedi in a matter of hours/days while ALL HIS LIFE he had been good and killing the Jedi enemies. So one answer is that he felt that by being Darth Vader and biding his time, he could kill Palpatine/Sidious and eventually take over the Empire and make it to his image (along with Luke, later on). But why be so brutal about it? Luke Skywalker (as well as Cade Skywalker, a 150+/- 10 years later) also became the Emperor's apprentice for a short while, but always was sabotaging the Emperor's efforts. In contrast, Vader seems to take pleasure in going against everything that he was taught and there is no explanation given as to why.

In the end, the force judges his final set of actions, helping kill Palpatine for the first time (presumably Palpatine was already in a cloned body but had never been really killed until then by anyone yet), along with all the cumulative good he did as Jedi, to be enough to give him redemption and he joins with Yoda and Kenobi. The implication is that there was always good in him, but yet for a long while, 20 years or so, Anakin Skywalker's Jedi training is barely present while Vader manifests his psychopathic self.

So the answer to "why" I think must lie in some kind of a split personality disorder. Anakin Skywalker was really two people, almost equally in balance with both light and dark, and when he was with the dark side, the light side was excluded entirely. I say "almost" because in the end he is with Yoda and Kenobi in light side heaven. So there is at least a small, yet significant, tilt even as he brings balance to the force for a brief while (almost all the Jedi except his son are killed; the Emperor who embodies the dark side is dead) and fulfills the prophecy of the chosen one.

It would be fun to psychoanalyse both Anakin Skywalker and Darth Vader and see what comes out of it. :)