Who becomes Darth Vader in Star Wars 3?

Answer 1

Anakin Skywalker, played by Hayden Christensen, goes completely over to the dark side when he sees his "mentor" Chancellor Palpatine get attacked by Jedi Master Mace Windu. Windu discovers that Palpatine is really the Sith master and goes to arrest him when Anakin walks in on them.
Anakin gets his name Darth Vader from Palpatine and calls him master.
When he looses a fight against Obi-Wan Kenobi on the planet Mustafar, getting his arms and feet cut off, he's so close to the lava that he actually catches flames. He's rescued by Palpatine and when he's so damaged he get's a suit or armor that gives him the distinct look in episode 4-6.