Bharathirajaa wanted actor Sivakumar to act in the lead role of Muthu / Dileep, over his assistant directors' objections. But after he narrated the story, Sivakumar rejected the offer, feeling it was not suitable for him despite liking the story. Kamal Haasan was eventually cast. He claims to have known the story of the film six years before shooting began. For his character's looks, Haasan wore "fitted suits with button-up shirts, ties" and flared bell-bottoms, in addition to "bright printed button-up shirts with enlarged collars and leather jackets". Haasan's looks in the film were inspired by the American serial killers Ted Bundy and Albert DeSalvo, while his "black leather jacket" was inspired by the one worn by Alan Arkin in Wait Until Dark (1967). Sridevi was cast as Sarada, collaborating with Bharathirajaa for the second time after 16 Vayathinile. Bharathirajaa initially cast Goundamani as a waiter and Bhagyaraj as the manager of Dileep's export company, but the actors later switched their roles. This was the feature film debut of Vadivukkarasi, who played Chitra. Bharathirajaa got a cat from his friend R. C. Prakash to portray Dileep's cat.
