Kadhalar Dhinam is a 1999 Indian Tamil romance film written and directed by Kathir. It is based on a relationship which begins through an internet chatroom and takes a turn after the protagonist has second thoughts about the relationship. The film featured newcomer Kunal Singh and Sonali Bendre in the lead roles, while Nassar, Manivannan, Goundamani and Chinni Jayanth appeared in supporting roles. The film produced by A.M. Rathnam, had music composed by A. R. Rahman and cinematography by P. C. Sriram. The original film was released on 9 July 1999, while a partially reshot dubbed Hindi version was released on 21 April 2000.
Kathir, being an inveterate surfer of the cybercafes of Chennai and Bangalore, decided to make a film on what he felt the internet could develop and be used for - romance. Kathir got to visit a newly opened cyber cafe in Bangalore and the "way that picture downloaded, slowly, frame by frame, was mind-blowing. Something struck me and I rushed out to write the basic one-liner of Kadhalar Dhinam". The film came as a successor to his 1996 blockbuster Kadhal Desam produced by K. T. Kunjumon. Since Rathnam was not aware about internet, Kathir created comedy track of Goundamani "to make it reach audiences".
Actor Shaam was amongst the auditionees for the debut lead role, before Kunal Singh was selected after Kathir spotted him outside a Bangalore cybercafe. The Pune-based, Kunal Singh, had been in Bangalore only to bulk up his body before joining the army, but with the offer chose to make a career in films. Kathir had scouted for a non-Tamil actress to play the lead role and subsequently Sonali Bendre was signed on to play the lead role in the film, making her debut in Tamil films. Isha Koppikar had also been considered for the film, but after finalising Bendre, Kathir then recommended her to his friend K. S. Ravi to cast her in his En Swasa Kaatre (1999). For the launch of the film, the makers flew in models Lara Dutta, Laila Rouass and Rani Jeyraj to attend the launch event of the film. Rambha appeared in an item number in the film. For a song sequence in the film, red rose petals were used to cover the forecourt of the Taj Mahal in Agra.
The film initially featured a different climax where Roja dies after taking tablets, but after release, the ending was altered to give a happy ending. The Times of India gave the film a negative review stating that "Kadhalar Dhinam is typically Kadhir. It's big, it's beautiful and it doesn't work." Indolink rated it 1.5 stars, citing, "Kaadhalar Dhinam needed to show a flair for a good story, screenplay and powerful dialogues. What Kadhir ended up with was a sagging script ... and a star cast whose characters lacked the necessary depth for this kind of a love story."
All lyrics written by Vaali; all music composed by A. R. Rahman.