Shankar conceived the film in mid-2003 during the post-production period of his previous film, Boys.
Shankar based the film on his own life experiences during his formative years when he was disturbed by what he saw around him, and his eventual displeasure with society.
Anniyan was initially thought to be Shankar's pet project - Robot - revived with a new title, but this was later proven not to be correct.
With the highest production value among Tamil films of its time, the film was touted to be the director's magnum opus and was labelled 'the most eagerly awaited film of the year' by the media.
Pre-production for Anniyan began in November 2003 and principal photography in March 2004.
The making of Anniyan, which included numerous production delays, took 14 months.
Shankar chose Vikram for the lead as he felt that the actor, in addition to being a performer, had the image of an action hero then.
Shankar further revealed during pre-production that Vikram was the 'life and soul' of Anniyan.
The heroine role of a 'devoted Iyengar Brahmin girl' was originally offered to Aishwarya Rai Bachchan, who was too busy to accommodate production dates.
After months of waiting for her call sheet, Shankar eventually offered the role to Sadha.
Mohan Vaidhya, a carnatic vocalist and occasional actor, plays a minuscule role as Sadha's father Krishna.
Malavika Avinash was approached to play Vikram's mother; she rejected the offer, stating, 'I am too young to do a screen mom and too old to be a heroine'
Comedian Charle played an unnamed wastrel and alcoholic who extorts money from his ageing parents for his expenses and is considered by Anniyan to be a liability to society.
Charle was instructed by Shankar, 'People should see only the character. Only later should they realise that it was Charle.'
The role of the younger Ambi was played by child actor Hari Prashanth alias Viraj.
When Hari came to the recording studio, he was accompanied by his father SN Surendar, a singer and dubbing artiste. Shankar recognised Surendar and asked him to dub for Nedumuni Venu.
Shankar, apparently impressed with Kanika's performance in Aethiree, asked her to voice for Sadha. She was selected among the thirty artistes, whose voices were tested.
The screenplay was written by Shankar and the film had dialogue written by writer Sujatha Rangarajan.
Shankar retained Sabu Cyril, his production designer from Boys, to handle the set design.
While the action sequences were orchestrated by Peter Hein and assisted by Stunt Silva, the dance sequences were choreographed by Raju Sundaram, Kalyan and Ahmed Khan.
Shankar chose Manikandan as the director of photography, impressed with his work in Main Hoon Na. Manikandan had earlier shot the 'Secret of Success' song in Boys.
Manikandan gave six months of bulk dates for the project; but, when the production was troubled by delays, Shankar demanded three more months to complete the film.
Manikandan walked out in October 2004 citing scheduling conflicts and Shankar replaced him with Ravi Varman.
Vikram allotted 18 months and 190 days of his call sheet for the film, including 165 days of bulk dates spread across six months.
Vikram credited his wife Shailaja Balakrishnan, a psychologist, for helping him in fleshing out the character of Ambi, a person who has multiple personality disorder.
Among the three shades to his character, Vikram found playing Ambi to be the toughest, reasoning, 'Because as a hero you are not used to being a wimp on screen. It's difficult to get beaten up.'
In contrast, being a graduate in English literature, Vikram found playing Remo much easier and more in his comfort zone.
Vikram later confessed that he had a tough time during the film's making as playing different characters affected him and he found himself going mad.
Vikram added that he would take a break after a 15-day shoot and watch the pigeons on his terrace as a way of dealing with the pressure.
Vikram grew a tummy to portray Ramanujam while he sported a 'macho look' for Anniyan.
Together with his character looks and those that he sported in the song sequences, Vikram appears in the film in 18 different getups.
Vikram's looks in the film was created by make-up artiste Banu.
For those parts that show him as metrosexual Remo, Vikram coloured his hair in streaks of copper and blonde.
Unwilling to reveal his 'new look' until the film was ready, Vikram avoided the media despite winning the aforementioned National Award for the year 2003
The officers from Central Board of Film Certification (Censor Board) had personally congratulated the director Shankar for making a bold movie that speaks to the society in a grand way.
Main inspiration for the movie was from Sidney Sheldon's famous novel 'Tell Me Your Dreams'.
The first Indian movie to be dubbed into French. Columbia Tristar bought the dubbing rights for broadcast in French-speaking nations.
About 200 (approx) still-cameras was used to create 'bullet-time' effect in particular fight scene.
This is the first movie directed by Shankar to not have music by A.R.Rahman.
Foreign fighters as well as martial artists from all over the state were used in the multi-opponent fight scene.
The stunt scene was shot at the JJ Indoor Stadium in Chennai over a period of 25 days.
This movie also borrows a story to Brad Pitt's Se7en, which has a similar plot of serial killer punishing habitual sinners.
With the use of sets, the art department recreated the Tyagaraja Aradhana near Mahabalipuram.
Shankar approached violin maestro Kunnakudi Vaidyanathan, a regular participant at the actual event, to conceive and orchestrate the Tyagaraja Aradhana sequence.
The film's tagline was 'He who comes from hell is not afraid of hot ashes.'
For filming scenes based on the punishments, buffaloes and snakes were transported in hundreds exclusively from Vellore and the sequence was shot for about 3 days.
The scene where Anniyan addresses a huge gathering was shot in a stadium in Hyderabad
The 'Anthakoopam' punishment sequence featuring the buffaloes was filmed in a set erected in Chennai's Prasad Studios. The animals were transported in 15 lorries containing 20 buffaloes each.
The film was budgeted at 263.8 million, making it at the time of its release the most expensive South Indian film ever made.
Anniyan was the first South Indian film to obtain institutional finance, and it had the highest insurance coverage available for films at that time.
The film, which won a National Award in the Special Effects category, grossed 570 million in its lifetime run.
