In "The Hobbit: The Desolation of Smaug," Fili was originally played—or, more precisely, originally cast—to be played by Robert Kazinsky. Kazinsky was announced as Fili in 2010, when Peter Jackson’s adaptation was being assembled as a two-film project. He left the production in April 2011 for personal reasons.
New Zealand actor Dean O’Gorman replaced him and portrayed Fili in the released Hobbit trilogy. Fili is one of Thorin Oakenshield’s nephews and a member of the Company of Dwarves, with Aidan Turner playing his younger brother, Kíli. Because the production changed actors during filming, some early footage and behind-the-scenes material can cause confusion about who ultimately appears as Fili.
The wording of the trivia question is commonly simplified: Kazinsky did not play Fili throughout the finished film, but he was the original actor attached to the role and was replaced during production. The final screen portrayal audiences see in "The Desolation of Smaug" is O’Gorman’s, alongside Richard Armitage as Thorin and Martin Freeman as Bilbo.