Following the success of the Hindi film
Special 26 (2013), its director
Neeraj Pandey revealed that he was approached by several filmmakers who were keen on producing a Tamil version of the film.
N. Lingusamy subsequently bought the rights of the film and planned to produce the venture in collaboration with Friday Filmworks, who had made the original version, but the project failed to materialise. In August 2014, producer
Thiagarajan announced that he had purchased the Tamil, Telugu, Malayalam and Kannada rights to remake
Special 26, and revealed that he would also direct all four ventures. Thiagarajan's son
Prashanth was revealed to be playing the lead role in Tamil, and by March 2015, Srikanth Ravichandran, then husband of television host
Dhivyadharshini, was expected to direct the film. After a period of little development, Prashanth revealed to the media in September 2015 that the film's shoot would commence soon after with
R. Madhesh as the director of the project. The film failed to materialise over 2016 and it was widely reported in the media that the remake rights of the original film had been transferred from Thiagarajan to
Studio Green and the film was to be made as
Thaana Serndha Kootam by
Vignesh Shivan with
Suriya in the lead role. The title was taken from a dialogue spoken by
Rajinikanth in
Baashha (1995). However, in February 2017, Thiagarajan insisted that the film was still being planned with Prashanth in the lead role. In late 2017, Thiagarajan made an application seeking an interim stay of the film's release, claiming that his studio Staar Movies still owned the film's rights. He stated that Staar Movies had entered into an agreement with the original producers,
Viacom18, in August 2014 and obtained the rights to remake the film in Tamil, Telugu, Malayalam and Kannada and that the agreement was valid for a period of three years. In early January 2018, the High Court refused the interim order application and called for the issues to be decided in a civil claim. Vignesh Shivan agreed to work on
Thaanaa Serndha Koottam at short notice, after another project,
Kaathuvaakula Rendu Kaadhal became delayed.
Studio Green's
K. E. Gnanavel Raja asked Vignesh to do a project to star Suriya and the team chose to use an earlier script planned by Vignesh on the
1987 Opera House heist, like
Special 26, where a group posing as
Central Bureau of Investigation (CBI) officers executed an income tax raid on the jeweller in
Mumbai, which he initially wanted to make with either actors
Sivakarthikeyan or
Vijay Sethupathi. The team claimed to legally purchase the remake rights of
Special 26, but instead of copying the film scene-by-scene, Vignesh was insistent that it was adapted to make it suitable for Tamil audiences. The film was announced to the public in September 2016, with principal photography starting in early November 2016.
Keerthy Suresh was signed on as the lead actress, while an ensemble cast of veteran actors including
Ramya Krishnan,
Suresh Chandra Menon,
Senthil and
Sudhakar were also a part of the first schedule. Suresh Chandra Menon initially dubbed in his own voice, but it was later replaced with
Gautham Vasudev Menon's voice. The film was predominantly shot across Chennai and Mysore, with the shoot finishing in August 2017. Post-production works for the film were completed at Knack Studios in Chennai. The film was also dubbed in Telugu as
Gang, with Suriya choosing to dub for himself for the Telugu version for the first time. == Music ==