The film tells the story of City Police Commissioner of Chennai, Irinjalakkuda Govindan Raghavan Maraar (I.G.Ragavan Marar) (Mohanlal) who gets an anonymous call. The caller (Kamal Haasan) demands that he release militants in exchange for information about many bombs planted across Chennai. The caller is serious as the police find a bomb planted very close to their headquarters. The commissioner is later cornered between releasing militants who had been responsible for killing innocent people and stopping bomb blasts around the city. Whatever he chooses forms the rest of the plot. Unnaipol Oruvan received positive reviews from the critics and was a commercial success. It was dubbed into Malayalam as Oru Budhanazhcha.
The recently dismissed police commissioner of Chennai, Maraar (Mohanlal) describes in a voice-over about his sudden termination due to a common man who walked into his life. An unnamed man (Kamal Haasan) is shown strategically placing a travel bag in a train in the Chennai Central railway station and in a shopping mall. He proceeds to place another bag, under the pretence of lodging an FIR, in the toilet of a police station in Anna Salai, Chennai. He then arrives on the rooftop of an under-construction building and sets up his base of operations, equipped with gadgets and instruments. He calls up Maraar and informs him that five bombs have been planted in locations throughout Chennai, which are programmed to explode simultaneously within four hours.
The caller demands that he would like to negotiate with a senior government official, who has the full authority. Maraar seeks the services of the chief secretary (Lakshmi) to act as the negotiator. Maraar also alerts his team involved in intelligence research and surveillance, tapping all the available resources in gathering preliminary information and tracing the location of the caller. Meanwhile, the caller tips off news reporter Natasha Rajkumar (Anuja Iyer), telling her to reach Anna Salai police station immediately.
Maraar initially suspects the caller to be bluffing, but his doubts are dispelled as the caller, to prove his seriousness and the police force's helplessness, reveals that a bomb has been planted in the Anna Salai police station. When the bomb disposal squad find the bomb, there is only three minutes left. They manage to deactivate the bomb after following the caller's instructions. Natasha reaches the scene on the caller's instructions and reports about the situation. An intense debate ensues between Maraar and the chief secretary on who would act as the negotiator with the caller. The chief secretary appoints Maraar as the State's negotiator with unrestricted power for one day. The caller talks full of life logics and religious philosophy and finally asks Maarar to release three convicted terrorists and one Hindu (a convicted arms seller), all who were arrested by him years ago.
Maraar's men realise that the caller is using advanced software to automatically switch the numbers and locations of his mobile phone SIM card every minute, rendering their manpower and the obsolete equipment useless and prompting them to employ the services of a young hacker, an IIT dropout. In the meantime, Maraar is able to obtain a facial composite of the caller with help of the police officer to whom the caller had approached to lodge the fake FIR, but much of the time passes without any concrete results on the identity or the location of the caller.
Ultimately, Maraar agrees with the caller's demand and puts two of his best men, Arif Khan (Ganesh Venkatraman) and Sethuraman (Bharath Reddy), in charge of handing over the four terrorists at the Sozhavaram airstrip. Once there, the caller confirms the identity of the four men via a conference call with Arif and Maraar. He then asks Arif and Sethu to unlock their handcuffs and leave them alone at a particular spot. Sethu orders his men to do as told but, at the last moment, Arif decides not to hand over terrorist Abdullah, to ensure all the information regarding the locations of the bombs can be forced out from the caller. Sethu argues with Arif and demands he do as ordered, but Arif forcefully grabs Abdullah and starts walking away. The other three enter a car which explodes soon after, killing them. But the caller knows that Abdullah is alive.
The caller threatens to blow up the remaining bombs across the city unless Arif and Sethu kill Abdullah. The Chief Secretary tells Maraar that the Chief Minister has to know about the current situation but Maraar disagrees and tells her that he will face the consequences, and orders Arif to kill the terrorist. Arif kills Abdullah and Sethu shoots Arif in the hand to make it look like an attack for self-defense. The caller confirms it via the news and reveals that he was bluffing and there are no more bombs anywhere in Chennai. He tells that as terrorism is instant, justice and safety must be so. Then Maarar questions the IIT hacker to trace the caller, but he refuses. But Maraar looks in the hacker's computer, discovers the location, and leaves abruptly towards the site. The caller, meanwhile destroys all of his gadgets with a mini-bomb inside a drum. As he leaves his hideout with all his camouflage, Maarar catches up to him.
Both shake hands; in a voiceover, Maraar says the caller told him his real name, but does not reveal it as it does not have any significance. He adds that the higher most officials saved themselves by framing him as a recluse and the CM fired him. Maraar admits that they all knew the caller was disturbed because of the insecure environment and the incompetence of the governing authorities but he never imagined him to go to such lengths and have the guts to do something like that. He also repeats that the facts of this incident cannot be found in any written record but only in the memories of those who actually witnessed it. He acknowledges that although the incidence has ambiguous moral significance, he personally feels that whatever happened, happened for the best.Mohanlal as Irinjalakkuda Govindan Raghavan Maraar (I. G. Raghavan Maraar), the Chennai City Police CommissionerKamal Haasan as the unnamed caller / common-manLakshmi as Chief Secretary of Tamil NaduGanesh Venkatraman as Arif KhanBharath Reddy as SethuramanAnuja Iyer as Natasha RajkumarPoonam Kaur as Anu SethuramanSanthana Bharathi as Karamchand LalaM. S. BhaskarPrem as ZakriaSriman as Arvind AdhavarAnand Krishnamoorthi as Arun the Hacker
While Kamal Haasan was cast in the lead role; confirmation of Mohanlal's presence in the film followed. Ganesh Venkatraman, who debuted in the 2008 film Abhiyum Naanum, was later confirmed for a supporting role. Bharath Reddy, who played a cop in the Telugu film Siddam, is playing another supporting cop role.
UTV Motion Pictures distributed the film along with Rajkamal International, Haasan's home production company, which produced it. Unnaipol Oruvan was directed by Chakri, a US-based filmmaker and a close friend of Haasan. Chakri had previously played the role of Govind's friend, Sai Ram, in Dasavathaaram, and the role of a child who takes still photographs of Kamal in the 1983 Telugu film Saagara Sangamam. Neeraj Pandey wrote the film's dialogue and screenplay. The music was composed by Kamal Haasan's daughter, Shruthi Haasan.
The title was changed from Thalaivan Irukkiran to Unnaipol Oruvan in early April 2009. Recent news in 2012 confirms that Thalaivan Irukkiran is a different film altogether, that is touted to be a multistarrer.
Unnaipol Oruvan started its first filming schedule on 6 February 2009. It completed shooting in 65 days.
It was initially set to release on 12 August 2009, since the date coincided with the release of Kamal Haasan’s first film Kalathur Kannamma and his entry into Tamil cinema in 1959, marking 2009 as Haasan's 50th year in cinema. However, owing to technical and administrative difficulties, the release was postponed to 18 September. The film was given a U/A (Parental Guidance) rating from the Central Board of Film Certification, mainly because of its theme — terrorism.
Unnaipol Oruvan received positive reviews from the critics. Sify said that technically the film was picture-perfect and that both Kamal Hassan and Mohanlal coming together is worth the ticket money. It mentioned that unlike in the Hindi version where Naseeruddin Shah had an edge over Anupam Kher, here the best dialogues were almost equally given to Mohanlal as well. Kamal Hassan' s performance and acting was well naturally received by critics.
Behindwoods rated that overall it was a brilliant work which will be appreciated by every socially responsible citizen of India. Indiaglitz commented that Unnaipol Oruvan deserves to be watched to see how Kamal & Mohanlal pit against Nasser & Kher. Kollywood Today praised that the movie was stupendously awesome and was a must-watch. Pavithra Srinivasan of rediff.com provided 4 stars and also had the same comments.
The music was composed by Shruti Haasan, daughter of Kamal Haasan. The album contains four songs and a remix. The songs are featured throughout the film. Kamal Haasan, singer Blaaze, and Manyusha Puthran contributed the lyrics. The audio launch was held on 6 September 2009 at Sathyam Cinemas.