Anakin Skywalker: "What have I done?" Darth Sidious: "You are fulfilling your destiny, Anakin. Become my apprentice. Learn to use the dark side of the Force. There's no turning back now." Anakin Skywalker: "I will do whatever you ask. Just help me save Padme's life. I can't live without her. If she dies, I don't know what I will do." Darth Sidious: "To cheat death is a power only one has achieved through centuries of the study of the Force. But if we work together, I know we can discover the secret to eternal life." Anakin Skywalker: "I pledge myself to your teachings. To the ways of the Sith." Darth Sidious: "Good. Good! The Force is strong with you, Anakin Skywalker. A powerful Sith you will become. Henceforth, you shall be known as Darth... Vader." Anakin Skywalker: "Thank you... my Master." Darth Sidious: "Lord Vader... rise."
This scene marks the transformation from Anakin Skywalker to Darth Vader. After helping kill Mace Windu, Anakin swears his allegience to Darth Sidious and officially joins the Dark Side.