Theeran Adhigaaram Ondru (transl. The Warrior: Chapter One) or simply Theeran is a 2017 Indian Tamil-language action thriller film written and directed by H. Vinoth and produced by S. R. Prakashbabu and S. R. Prabhu under the banner Dream Warrior Pictures. Based on the incidents from the Operation Bawaria case, it depicts the nefarious activity of dacoits and its eventual containment with the Tamil Nadu Police squad headlined by DGP S. R. Jangid. The film stars Karthi, in the titular character Theeran, modelled on Jangid, alongside Rakul Preet Singh and Abhimanyu Singh, who plays the main antagonist.

Vinoth had planned for the script based on the incident even before his debut film Sathuranga Vettai (2014), but he later worked on the project in late-2014. To research further, he had met many police officers who handled the similar cases. Following an official announcement in December 2016, principal photography commenced in January 2017 and ended that July. Filming took place in many real locations across Chennai and North India, in order to capture the authenticity of the film and has been shot in locations where the incident happened. The film's cinematography was handled by Sathyan Sooryan and editing done by Sivanandeeswaran. Ghibran composed the soundtrack and film score.

The film, distributed and co-produced by Reliance Entertainment, released worldwide on 17 November 2017. The film opened to critical acclaim, praising the direction, writing, cinematography, soundtrack, musical score and the cast performances—especially that of Karthi. The authenticity of capturing the incidents, along with the realistic portrayal of Tamil Nadu Police in fiction was highlighted and praised by critics. As per source it was a box-office success, grossing ₹96 crore In addition, the film won an Ananda Vikatan Cinema Awards and Techofes awards, two Edison and Vijay awards each. It received three nominations at the South Indian International Movie Awards and five Filmfare Awards; the film's only win was Best Tamil Actor (Critics) for Karthi. Film Companion ranked the film as one of the '25 Greatest Tamil Films of the Decade' and Karthi's performance among '100 Greatest Performances of the Decade'.On October 2023, a sequel was announced.