Aalavandhan (transl. The one who came to rule) is a 2001 Indian psychological action thriller film directed by Suresh Krissna and produced by S. Thanu. An adaptation of the novel Dhayam that was written by Kamal Haasan in 1984, The film stars Haasan in dual roles, with Raveena Tandon, Manisha Koirala, Sarath Babu, Gollapudi Maruti Rao, Madurai G.S. Mani and Milind Gunaji in supporting roles. It has elements of magic realism.
 The film was simultaneously shot in Hindi with the title Abhay (transl. Fearless) with three different actors. Although a commercial failure during its release, Aalavandhan and Abhay won the National Film Award for Best Special Effects. A digitally restored version was  released on December 8, 2023.
 Major Vijay Kumar and his group of the Black Cats save a group of tourists held hostage by terrorists in a Kashmir valley. Meanwhile, at a military hospital, Vijay meets his girlfriend Tejaswini aka Teju, a news presenter who he is ready to marry. Teju reveals she is pregnant after she presents her HCG report to Vijay after one of their dates gone wrong. Vijay then reveals to Teju about  his plan to visit his twin brother, Nanda Kumar alias Nandu, in a mental asylum who is incarcerated for murdering his stepmother Jayanthi.
 Nandu is a cleverly scheming and with good physical strength, yet paranoidal schizophrenic man who has spent most of his life in the asylum, often communicating using metaphors and poetic expressions. Vijay cares about Nandu and looks forward to his release, but Nandu's doctor tells him that Nandu has developed into a psychopath. He is now a danger to society and should not be released.
 Vijay and Teju visit Nandu to share the news about their impending marriage, which turns disastrous as Nandu begins to see Teju in the image of their Jayanthi. Seeking to save Vijay from Teju, Nandu manages to escape custody after killing two other inmates Sulthan and Paasha, for a clean getaway, thus leaving no trail. He later meets his maternal uncle, who was responsible for incarcerating him. The man dies of choking upon seeing his nephew. Vijay and Teju get married. The next day Vijay and Teju are shocked to learn of Nandu's escape. Vijay initially refuses to believe it was Nandu who escaped. But, Nandu's doctor believes it was Nandu who escaped, because of the similarity that both Nandu and his murdered buddy Sulthan are circumcised due to health reasons after the postmortem of Sulthan's beheaded corpse, thus proving Nandu is circumcised. Later, Vijay is convinced that it was Nandu.
 Nandu visits Vijay's home when he is not there and leaves a message about wanting to kill Teju. He keeps hallucinating his deceased mother in his imagination. While searching for Teju, Nandu kills a drug peddler and falls in love with a socialite Sharmilee by looking at her promotional posters. By chance, he stumbles across Sharmilee at a hotel. Sharmilee ecstatically falls for Nandu upon his antics, and both become close. Both being drugged, Sharmilee playfully whips Nandu, which inadvertently causes him to visualise Jayanthi's whippings and brutally murders her as a result. After returning to his senses, he regrets his actions and tearfully burns Sharmilee's corpse before exiting the room, but leaves behind evidence through which Vijay deduces him as the murderer.
 Vijay and Teju leave for Vijay's ancestral home in Ooty to stay safe from Nandu, but he secretly follows them. Vijay and Teju find Nandu's old diary in the house through which they read his past: Vijay's and Nandu's mother Priya committed suicide after realising that Santhosh, their father was having an affair with Jayanthi, who later became their stepmother. Both brothers hate her, especially Nandu. The teacher complains about this, and Nandu justifies that he is only reflecting the home environment. Enraged, Santhosh beats both his sons for disliking his new wife.
 One day, Vijay learn that Jayanthi is having an affair with another man and Nandu tries telling this to his father, who pays no heed, and instead beats him. Nandu pleads to his maternal uncle to take him along with him. But as he is suffering from throat cancer, he refuses and suggests a boarding school. Eventually, Vijay leaves with his uncle to a boarding school while Nandu remains home.
 The situation gets worse at home with Nandu and Jayanthi turning violent, and Santhosh gets a heart attack. Nandu overhears a conversation between Jayanthi and a lawyer, and realises that she is only after his father's wealth. Seeing this, Santhosh dies due to another heart attack. Nandu now starts to see both his deceased parents in his hallucinations, as a result of being turned into a psychopath due to his Jayanthi's cruel antics. His mother gives him the mission of killing Jayanthi, granting him a military knife. Nandu stabs Jayanthi with the knife, but before dying, she vows that she will return. Nandu stays with Jayanthi's corpse in the house before being incarcerated at the asylum.
 In the present, Vijay learns from his old friend Tenoosh Kooth that Nandu has reached Ooty. Vijay reaches on time to save Teju from Nandu, who entered their hotel room and leaves with her. Nandu, after getting a serpent styled tattoo all over his body which resembles the bond between the brothers by Tenoosh Kooth, decides to exact revenge on Teju. He chases the couple wreaking havoc across the road. After a while, they escape from the clutches of Nandu, Vijay manages to push Nandu's car into an abyss and assumes he is dead. However, Nandu escapes and continues his trail. Vijay plans to leave the city and notices Nandu coming to the hotel secretly.
 Vijay and his commandos try to nab him, but he takes on everyone and kills many. Finally, the brothers have a fight where Nandu overpowers Vijay. He corners Teju, who starts whacking him with a belt in self-defense, reminding Nandu of Jayanthi's manner of punishing him. Vijay reaches by then, and there is another fight between the brothers. Nandu visualises his mother asking him to join her as Jayanthi is torturing her up there. He realises his mistake and apologises to Vijay for chasing Teju. To kill Jayanthi, he lights up some gas cylinders which explodes and kills Nandu.
 Some months later, Teju is revealed to be pregnant with twins. She fears they will have the same traumatic childhood Vijay and Nandu had, but Vijay comforts her by telling her that they shall provide good parental care and such thing will not happen.
 All characters mentioned above in the Tamil version are the same in the Hindi version except Nandu's name, the doctor's character, and Tejaswini's parent's characters have been played by different actors.
 Dhayam was a novel written by [Kamal] for a magazine long back, and it talked about a pair of twin brothers, one being an ‘animal’ (Nandhu) and the other a ‘trained animal’ (Vijay). We wanted this contrast and started off from there. The ‘animal’ had to literally look the part, and that's why Kamal sir went bald and bulked up like never before [...] The ‘trained animal’ was a dashing commando with a logical approach. Usually, most twin films fail to show the real difference between both brothers. To bring out this contrast, Kamal shot for Vijay first and then took on the Nandhu character.
 —Suresh Krissna, in 2017
 In the early 1980s, Kamal Haasan wrote a story titled Dhayam for the journal, "Idhayam Pesugiradhu". He had discussed making the story into a film with K. Balachander during the period, but felt that the story was ahead of its time. In 2000, he picked up the story again and agreed to make the film with director Suresh Krissna, a former assistant of Balachander, and producer S. Thanu. When Thanu had agreed to produce a film for Haasan, he had initially rejected the storylines of Pammal K. Sambandam and Nala Damayanthi. This prompted the pair to begin work on Dhayam instead, and the film was revealed to be called Aalavandhan in Tamil and Abhay in Hindi. Abhay was distributed by reputed Shringar Films. Mahesh Mahadevan was signed on to compose the background music, Tirru was selected to be the cinematographer and Sameer Chanda was picked to be the art director. Actor Jayam Ravi also worked on the film as an assistant director.
 The film was first announced with Haasan and Simran  and Bollywood actress Rani Mukerji in a special appearance. Both actresses left the project for its delay in start, being replaced by Raveena Tandon and Manisha Koirala. Producer Dhanu had initially tried to cast Aishwarya Rai in the film, but the actress did not sign the project.
 Composer Harris Jayaraj was first approached by the producer to do music for the movie, and he assured to introduce him as a music composer before Minnale. But Harris refused as he owed to do his first movie with Gautham Vasudev Menon. Later, music trio Shankar–Ehsaan–Loy was signed as music composers.
 The film featured Haasan in two distinct roles, for one of which he had his head shaved bald and gained ten kilograms. To play the other in the film, he went to the National Defence Academy for a crash course and also consulted his co-actor Major Ravi, who was a former officer in the Indian Army.  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. Another fight sequence was shot in Delhi for 15 days using 39 cars with 3 cameras with a machine called Airramp brought from abroad for jumping scenes.
 The soundtrack of the movie was composed by the music trio Shankar–Ehsaan–Loy making their debut in Tamil, and the film score is composed by Mahesh Mahadevan. The film features six tracks in both Tamil and Hindi 
versions with lyrics written by Vairamuthu and Javed Akhtar respectively.
 The album of the film's Tamil version was released on 24 September 2001, and it created a record by selling over 2,00,000 copies in less than eight hours of its release. However, according to Rediff, it "did not live up to expectations."
 All tracks are written by Vairamuthu All tracks are written by Javed Akhtar Started on a budget of ₹7 crore, the costs associated with Aalavandhan tripled by the time of release. The film was released on 16 November 2001, during Diwali. The Hindi version Abhay was bought over in Maharashtra by the reputed Shringar Films. The number of prints in Tamil Nadu had been increased by almost 5 times the average. Both Aalavandhan and Abhay got A (adults only) certificate from the CBFC. Later, both were re-examined upon request to get a UA certificate.
 The film was the top opener of the Diwali weekend at the box office but was not successful. According to Bollywood Hungama, Abhay collected ₹2.02 crore at the box office.
 Initial reviews at the time of the film's release were mixed. Malathi Rangarajan of The Hindu said, "Too much publicity can sometimes affect a film adversely, because of the great expectations triggered. In the case of Aalavandhan, the hype and hoopla built up for months seems justified — to a certain extent". Visual Dasan of Kalki praised the acting of Haasan, music, visual effects, flashback, cinematography and editing. The film won the National Film Award for Best Special Effects at the 49th National Film Awards in 2002.
 Reviewing the Hindi version Abhay, Taran Adarsh said, "On the whole, Abhay has nothing to offer to the masses or the classes. Poor". Rediff author R. Swaminathan said, "What happens when an exceptionally talented actor develops an inexplicable urge to delve into the dark side of the human psyche, and worse, decides to paint the town red about it? Well, for one, you get a film called Abhay."  Vijay Ramanan of Planet Bollywood rated the film 5.5 out of 10, saying, "The film falls flat on its face because of its failure in the two most important departments of filmmaking – scriptwriting, and direction [...] It almost seems as if Kamal Haasan and Suresh Krishna were high on drugs while making this film." Smriti Kashyap of fullhyd.com said "The movie is a huge letdown. It lacks the pop, snap and crackle to fill you with enough guts to potter down to the theater and watch it. Catch it on the CD, it's easier on the brains."
 Although the film failed commercially, it was positively received over the next few years, subsequently becoming a cult classic, with some critics stating that the film was "way ahead of its time". The film was shown in the 2016 Fantastic Fest, where it was acclaimed by the American audiences. In 2013, Rediff included the film in its list, "The 10 Best Films of Kamal Haasan".
 National Film Awards
 Tamil Nadu State Film Awards
 Following the film's positive response at the 2016 Fantastic Fest, a digitally restored version was announced. On 25 January 2023, it was announced that the film would release in over 1000 screens, although no release date was provided. In November 2023, Thanu announced that the film is  released on December 8, 2023.
 In April 2021, Thanu announced that he would release a re-edited version of Aalavandhan.
 The song "Kadavul Paathi Mirugam Paathi" inspired a 2015 film of same name directed by Raaj Menon.