Kaththi (transl. Knife) is a 2014 Indian Tamil-language action thriller film written and directed by AR Murugadoss. It is produced by Subaskaran Allirajah's Lyca Productions. The film stars Vijay in dual roles, alongside Samantha, Neil Nitin Mukesh, Tota Roy Chowdhury, Sathish, Sudip Mukherjee, Rama, and Jeeva Ravi. In the film, a petty thief assumes the identity of his lookalike and attempts to lead a rebellion by farmers from the latter's village, Thanoothu, and helps them fight against an entrepreneur who exploited Thanoothu's water resources.

The film was officially announced in November 2013, and principal photography took place between February and September 2014. Primarily shot across Chennai, it was also filmed in Kolkata, Mumbai, Hyderabad, Rajahmundry, Begumpet, Nellore, and Kadapa. The cinematography was handled by George C. Williams, and the film was edited by A. Sreekar Prasad. The music is composed by Anirudh Ravichander. The film marks the Tamil debuts of Mukesh and Chowdhury.

Made on a budget of ₹70 crore, Kaththi was released worldwide on 22 October 2014, coinciding with Diwali, and received critical acclaim. Before the film's release, it faced controversies for plagiarism allegations, and the business link of Subaskaran, the film's producer, with Sri Lankan president Mahinda Rajapaksa, which resulted in Tamil fringe groups protesting against the film. Despite this, the film was a commercial success, grossing around ₹128 crore (equivalent to ₹205 crore or US$24 million in 2023), and was remade into Telugu as Khaidi No. 150 (2017).

A recipient of various accolades, the film won three out of seven nominations at the Filmfare Awards South, including the Filmfare Award for Best Film – Tamil. It won four SIIMA (including Best Film) and two Vijay Awards (Favourite Film and Favourite Director for Murugadoss). Additionally, the film won an IIFA Utsavam and Ananda Vikatan Cinema Awards each, three Edison Awards and a nomination for Best Social Awareness at the Norway Tamil Film Festival Awards before eventually losing to Sigaram Thodu (2014).