Kaththi (transl. 'Knife') is a 2014 Indian Tamil-language action drama film written and directed by AR Murugadoss and produced by Lyca Productions. The film stars Vijay in dual role with Samantha, Neil Nitin Mukesh, Tota Roy Chowdhury and Sathish. It focuses on Kathiresan, a petty thief and lookalike of Jeevanantham, who assumes the identity 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.

It marks the second collaboration of Vijay and Murugadoss, after Thuppakki (2012). The official announcement took place in November 2013, and the principal photography took place in February—September 2014. Primarily shot across Chennai, it was also filmed in Kolkata, Mumbai, Hyderabad, Rajahmundry, Begumpet, Nellore and Kadapa. The cinematography for the film was handled by George C. Williams and the film was edited by A. Sreekar Prasad. The soundtrack and film score is composed by Anirudh Ravichander.

Made on a budget of ₹70 crore, Kaththi was released worldwide on 22 October 2014, coinciding with Diwali, and received critical acclaim with critics praising Vijay and Neil's performance, technical aspects, background score, soundtrack, cinematography, editing, action sequences, social message, direction and the writing. 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 Tamil fringe groups to protest against the film. Despite this, the film was a commercial success, grosing around ₹100—128 crore (equivalent to ₹159—204 crore or US$20–26 million in 2023), and was remade into Telugu as Khaidi No. 150 (2017), starring Chiranjeevi.

A recipient of various accolades, the film won three out of seven nominations at the Filmfare Awards South, including 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 losing eventually to Sigaram Thodu (2014).