Ko (transl. 'King') is a 2011 Indian Tamil-language political action thriller film directed by K. V. Anand, and written by him and the duo Subha. The film stars Jiiva, Ajmal Ameer, Karthika Nair (in her major Tamil debut), and Piaa Bajpai, while Prakash Raj and Kota Srinivasa Rao appear in supporting roles.The film follows Ashwin (Jiiva), a photojournalist working for Dina Anjal who covers the Tamil Nadu State Election.

The film features music composed by Harris Jayaraj, with cinematography handled by Richard M. Nathan and editing done by Anthony. The film was released on 22 April 2011 to mostly positive reviews, and became a commercial success. It was dubbed in Telugu as Rangam, and released on the same date, which also becoming a success at the box-office.

The film won two Filmfare Awards South, three Vijay Awards, two SIIMA Awards, and four Tamil Nadu State Film Awards. Based on an online poll conducted by The Times of India, it won the Chennai Times Best Film Award for 2011. The film was remade in Bengali as Kanamachi (2013). A standalone sequel to the film titled as Ko 2 was released in 2016, with Prakash Raj reprising his role.