Star Wars: Episode III (2005) - Enter Darth Vader
After being seduced to the dark side, Anakin Skywalker (Hayden Christensen) pledges himself to the teachings of his new master, Darth Sidious (Ian McDiarmid). The newly anointed Darth Vader is then given a simple mission by his master, to kill every Jedi in the temple, "do what must be done Lord Vader... do not hesitate, show no mercy." Vader and a legion of clone troops march on the Jedi Temple killing every living thing.
In the moments that follow we finally get an answer to the mystery that has lingered for 25 years, how did good Anakin Skywalker become evil Darth Vader? Very shortly we will have our answer. As the destruction of the Jedi Temple continues Vader enters the council chambers, it is full of frightened children. One of the young Jedi approaches and asks a question, "Master Skywalker, there are too many of them, what are we going to do?" The child receives no reply, except for the hiss of the light saber as it comes to life. Although not shown, we are left with no doubt of the answer the boy and his companions received. The film would go on to show the final climatic fight with Obi-Wan Kenobi (Ewan McGregor) and how Vader got his now iconic look. But forget all that, this is the true moment Darth Vader is born; you can't kill a whole room full of "younglings" and ever go back again.