Jyothika was considered for the role done by Sonia Agarwal initially. The film was later remade in Telugu in 2004, as Nenu with Allari Naresh and Veda replacing Dhanush and Sonia Agarwal, respectively. It has also been remade in Kannada in 2009, as Ravana with Yogeesh Hunsoor and Sanchita Padukone in the lead, and in Bengali in 2010, as Amanush starring Soham Chakraborty and Srabanti Malakar. The film was also remade in Bangladesh in 2004 as Onno Manush directed by Kazi Hayat starting Kazi Maruf, Shabnur and Shakil Khan.
The story explores the mind of a youth who is mentally and physically abused in his childhood. The lack of a mother's love haunts the protagonist throughout the film as the girl of his infatuation is killed. Becoming a psychopath, he desperately tries to woo his newly found lady love and his efforts culminate in a superb nail-biting cliffhanger.
Vinod (Dhanush), who has grown up under the care of a church father (Nagesh), is an introvert but a genius. He is forcibly sent to college by the father but is a complete misfit in class. Though shunned by the rest of his class, Divya (Sonia Agarwal) becomes his friend and he gradually warms up to her. His feelings soon turn into love but he realizes that Divya considers him as only a friend and learns that Divya is in love with another classmate, Aadhi (Sudeep Sarangi).
Divya's father is enraged on learning about her love. He locks her up and prevents her from contacting anyone. Vinod comes and requests to meet her on the pretext of getting some old clothes for himself to wear. Pitying Vinod, her father allows him to meet Divya. Vinod escapes with Divya and convinces her that she will meet Aadhi at Ooty.
Vinod has set up a secret place in Ooty for executing his plan of wooing Divya. He makes her stay with him, while convincing her by talking about Aadhi's arrival. On one such day, he reveals his miserable past, when he was made to work for paid labour after being orphaned at an early age. He revolts against the oppression one day. Promptly he is beaten black and blue for his profanity. Moreover he also loses his girlfriend to rapists in that place, who also kill her. After some days he kills the woman running the orphanage and also kills the rapist, helped by other children. They manage to break the place and escape from there and seeks refuge in the place of a church father.
Divya is touched by his past. Incidentally the police and Aadhi arrive at the place. While Vinod was away to get some food, they try to explain to Divya that Vinod is a psychopath. Yet Divya scoffs at their claims, citing his gentlemanly behaviour over the days she has been alone with him. Vinod, learning that the police have arrived at the scene, begins to indulge in violence. He opens fire, killing a police constable. Forcing them out of their hideout, he manages to evade the police Inspector and Aadhi and successfully brings Divya back to their original place of stay.
Divya soon identifies the tiger in the cow's skin. Vinod pleads with her, telling her that all he wanted in his life was her presence. But Divya called him a friend and stated her inability to accept him as her partner for life.
Meanwhile Aadhi regains consciousness and comes back to attack Vinod and rescue his girlfriend. A violent fight follows, where Vinod defies his puny self and treats Aadhi with disdain. The fight culminates with Vinod, Aadhi and Divya teetering at the edge of a slippery cliff.
While Divya clutches a tree bark tightly, Vinod and Aadhi slip out and barely manage to hold either of her hands. Divya is forced to choose between her boyfriend and friend. Aadhi's pleas notwithstanding, Divya does not have the heart to kill Vinod, who smiles wryly at Divya and lets go of her hands himself, falling to his death in the abyss.Dhanush as Vinod
Sonia Agarwal as Divya
Sudeep Sarangi as Aadhi
Nagesh as Father Rozario
Daniel Balaji as Police Inspector
Sreekanth as Divya's father
Following the success of the previous film Thulluvadho Ilamai (2002), the team chose to collaborate again with the psychotic romantic thriller Kaadhal Kondein, credited as Selvaraghavan's first film with Dhanush and Jyothika in Lead roles. The venture, produced by his home production, also marked the first collaboration of Selvaraghavan with cinematographer Arvind Krishna, whom he would later associate with New Comer Sonia Agarwal was replaced Jyothika. Selvaraghavan had written the script for the film in the late 1990s and had first narrated the story to Dhanush in their shared bedroom at home, before asking him to play the lead role of Vinod.
For Kaadhal Kondein, director Selvaraghavan and music composer Yuvan Shankar Raja came together again after their earlier successful collaboration in Thulluvadho Ilamai (2002), for which Selvaraghavan worked as a writer. The soundtrack of Kaadhal Kondein released on 20 March 2003, featuring seven tracks with lyrics written by Pazhani Bharathi and Na. Muthukumar. The music, especially the film score, received universal critical acclaim, establishing composer Yuvan Shankar Raja as one of the "most sought after music directors" in the Tamil film industry.
More than one year after the release of the film, an "original soundtrack" was released, that followed the Hollywood-style. It was said to be the first time, that an original soundtrack was released for a film in India as the soundtracks released in India do not contain any film score pieces but full songs that feature in the film itself. The OST of Kaadhal Kondein contains 20 tracks overall, which includes the seven earlier released tracks, four "montage" bit songs, that featured in the film, but not in the soundtrack, and nine pieces from the actual film score, which were titled as "Theme Music".
All music composed by Yuvan Shankar Raja.
The film opened in July 2003 to unanimously positive reviews, with a reviewer from The Hindu noting "his story, screenplay, dialogue and direction are focussed and hit the bull's eye straightway — hardly missing the mark." The film became successful at box-office grossing ₹6 crore worldwide.2004: Filmfare Best Female Debut (South) - Sonia Agarwal
2004: Filmfare Best Director Award - Selvaraghavan
Since its release, the film has been remade into several Indian languages, while Selvaraghavan was briefly associated with the Hindi remake to be produced by Boney Kapoor in 2004, but the project did not eventually materialise. The film was later remade in Telugu in 2004, as Nenu with Allari Naresh and Veda replacing Dhanush and Sonia Agarwal, respectively. It has also been remade in Kannada in 2009, as Ravana with Yogeesh Hunsoor and Sanchita Padukone in the lead, and in Bengali in 2010, as Amanush starring Soham Chakraborty and Srabanti Malakar. The film was also remade in Bangladesh in 2004 as Onno Manush directed by Kazi Hayat starting Kazi Maruf, Shabnur and Shakil Khan.
The film provided career breakthroughs for both Selvaraghavan and Dhanush in the Tamil film industry. The success of the song "Devathaiyai Kandaen" prompted Boopathy Pandian to name his 2005 film starring Dhanush after the song title.