The film follows the life of Kyle, who became the deadliest marksman in U.S. military history with 255 kills from four tours in the Iraq War, 160 of which were officially confirmed by the Department of Defense.
電影跟隨凱爾的生活，凱爾為美國軍事史上最致命的狙擊手，在伊拉克戰爭中的4次任務中射殺255人，其中160次獲美國國防部正式確認。