Conversation so far:
Was Hayden Christensen in Star Wars?
Hayden Christensen announced that he would be starring as Anakin Skywalker in Star Wars: Episode II Attack of the Clones and Star Wars: Episode III Revenge of the Sith
What year did Hayden Christensen announce that he would be starring as Anakin Skywalker in Star Wars: Episode II Attack of the Clones and Star Wars: Episode III Revenge of the Sith happen?
Hayden Christensen announced he would be starring as Anakin Skywalker on On May 12, 2000.
Did anything happen to Hayden Christensen on the set of Star Wars?
Hayden Christensen asked George Lucas if a special Vader suit could be constructed to fit his own body, rather than have a different actor.
Did George Lucas  make that special Darth Vader suit for Hayden Christensen?
george Lucas agreed and suit was engineered to fit Hayden Christensen's frame, even including extensions to allow for the actor to attain Vader's 6 ft 6 inches.
Did the Star wars fans like Hayden Christensen as Darth Vader?
What else happened while Hayden Christensen was filming Star Wars besides him asking George Lucas to create his own custom Darth Vader suit?
When Revenge of the Sith was being produced, Hayden Christensen and Ewan McGregor began rehearsing their climactic lightsaber duel long before Lucas would shoot it.

Question: Why did they choose Hayden?
Self-contained rewrite: Why did George Lucas choose Hayden Christensen?