Mersal (transl. Zapped) is a 2017 Indian Tamil-language action thriller film directed by Atlee and produced by Thenandal Studio Limited, in the studio's hundredth film production. The film stars Vijay in triple roles, alongside S. J. Suryah, Kajal Aggarwal, Samantha Ruth Prabhu and Nithya Menen. Sathyaraj, Vadivelu, Hareesh Peradi, Kovai Sarala and Sathyan play supporting roles. It is the second out of the three collaboration between Vijay and Atlee, before they began working with others. The film follows two brothers who were separated after the younger one's birth; Vetri, a vigilante magician who is against the medical crimes and Maaran, a reputed doctor who charges meagre amounts from his patients.

The film's principal photography commenced on 1 February 2017, at Chennai and was completed in September 2017, within 130 working days. Filming took place on Gdańsk, Poland and Jaisalmer, Rajasthan. The background score and soundtrack album were composed by A. R. Rahman, while the cinematography was done by G. K. Vishnu and edited by Ruben.

Mersal was released worldwide on 18 October 2017, coinciding with Diwali. The film received mostly positive reviews with critics praising the performances of Vijay, Menen and S. J. Suryah, A. R. Rahman's soundtrack, cinematography, social message and Atlee's direction, but criticised the cliched plot and excessive length. It is also a recipient of various accolades. The film was a commercial success, grossing ₹200 crore (US$23 million)–₹260 crore (US$30 million) worldwide, becoming the highest-grossing film in Vijay's career at that time as well as one of the highest-grossing Tamil films. The film completed 100-day theatrical run on 25 January 2018. The film was released on 6 December 2018 in China by HGC Entertainment. Due to demand, the film was screened at the largest cinema theatre in Europe Grand Rex, France. The film was screened at the Hainan International Film Festival in Hainan, China and at the Bucheon International Fantastic Film Festival in South Korea.