Anniyan (transl. Stranger) is a 2005 Indian Tamil-language psychological action thriller film written and directed by S. Shankar and produced by V. Ravichandran of Aascar Films. The plot centres on a disillusioned everyman whose frustration at what he sees as increasing social apathy and public negligence leads to a split personality that attempts to improve the system. Vikram stars as Ambi, an idealistic, law-abiding lawyer who has Dissociative identity disorder (formerly known as Multiple personality disorder) and develops two other identities: a suave fashion model named Remo and a murderous vigilante named Anniyan. Sadha plays the female lead role. Actors Vivek, Nedumudi Venu, Nassar and Prakash Raj also featured in the film.

Shankar conceived the film in mid-2003 during the post-production period of his previous film, Boys. He 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 the society. Pre-production for Anniyan began in November 2003 and principal photography in March 2004. The making of the film, which included numerous production delays, took 14 months. The film was shot at Hyderabad, Thanjavur, Tindivanam and Chennai, and the song sequences were filmed in Mumbai, Malaysia, Amsterdam and Tenkasi. The film was notable for its recreation of the Tyagaraja Aradhana music festival and the extensive use of time slice photography in an action sequence.

Cinematographer V. Manikandan abandoned the project halfway through, until he was replaced with Ravi Varman. The technical departments were headed by V. T. Vijayan (editing), Sabu Cyril (production design), and Peter Hein (stunt choreography), and the soundtrack was composed by Harris Jayaraj, who was in his first collaboration with the director. The film was touted as the director's magnum opus and was budgeted at ₹263.8 million, making it at the time of its release the most expensive South Indian film ever made. Notably, it was the first South Indian film to obtain institutional finance, and it had the highest insurance coverage available for films at that time.

Originally filmed in Tamil, and released simultaneously in the 4 South Indian states on 10 June 2005, the film was dubbed into Telugu as Aparichithudu and Hindi as Aparichit The Stranger, was released a year later on 19 May 2006. Further, the film was also dubbed into French and released in French-speaking countries worldwide by Columbia Tristar. The film received positive reviews from critics and became a commercial success across South India. In addition to winning a record breaking eight Filmfare Awards and six State Film Awards, the film also won a National Award in the Special Effects category.