The film was inspired by the story Dhayam, which Kamal had written for Idhayam Pesugiradhu, in 1984. KB had earlier rejected the offer of adapting it into a film saying it was way ahead of its times.
The original story Dhayam by Kamal Hassan was about twin brothers one being an animal another a trained animal. To differentiate between the two, he went bald for the negative character.For playing Nanda, the schizophrenic with delusions of grandeur, Kamal gained 10 kgs and went naked for a scene, which eventually was chopped off by the censor board.For playing the role of Major Vijaykumar, Kamal took a one month-crash course in the National Defence Academy.Stunt choreographer Grant Page, who had worked in the American film It's a Mad, Mad, Mad, Mad World, was assigned to compose stunt sequences in Kashmir.The climax fight sequence was shot in Delhi for 15 days using 39 cars with 3 cameras with a machine called 'Air Ramp' brought from abroad for filming the jumping scenes.The film was made at a budget of 22 crores, the highest for a Tamil film at the time.The scenes where both Vijay and Nandhu characters appear were not done with the traditional matte or masking shots technique, which always involved static shots, which meant the camera would not move.Kamal decided not to use any static shots for both characters to appear in, and instead went for a motion-control rig to mount the camera on and film these sequences with shifting camera angles.This expensive rig did not exist in India, so it had to be imported from Australia. This was the first time an Indian film used a motion-control rig.This meant that the same sequences were filmed twice; first with Vijay Kumar and, weeks later, with Nandhu. The output was stunning from both a cinematographic and technical standpoint.The 20-minute psychedelic acid-trip that Nandhu embarks on is presented to us in real time in all its twisted perfection, so much so that it starts getting into our heads. Never before. Never after.At a time when animation was still looked down as cartoons, Kamal resorted to graphic animation to get away with extended sequences of unimaginable barbarity. It was executed to utmost perfection.Hollywood director Quentin Tarantino's admitted in an interview that he was inspired by Aalavandhan to create the animated fight sequences for his 'Kill Bill' films.Because Kamal carried two different looks, filming was done twice to incorporate both characters in the same scene, which meant that sets were recreated exactly, complete with all the minute details.Aalavandhan (Abhay in Hindi) won the National Film Award for Best Special Effects for its creative execution of live and animated special effects, which enhance the dramatic impact of the film.Kamal Hasaan's evil twin character was initially suppose to be exactly based on Anthony Hopkins's character of Hannibal. But Kamal got cold feet and removed the cannibalism part of the character.Aalavandhan's album (by Shankar-Ehsaan-Loy) created a record by selling over 2,00,000 copies in less than eight hours of its release.Nawazuddin Siddique worked as a dialogue coach during Abhay (2001). He helped some of the south actors deliver their lines in Hindi.The number of prints in Tamil Nadu was increased by almost 5 times the average for Aalavandhan's release.15 years following its release, the film was screened at the 2016 Fantastic Fest in US, where it opened to unexpected critical acclaim by all the audiences, most of which were non-Indian Americans.Following the film's positive response at the 2016 Fantastic Fest, a re-release of a digitally restored version was announced.