Kamal Haasan, Saranya, Karthika
Sakthivelu "Velu" Nayakan is born to an anti-government union leader (Kitty). The child, Velu, is tricked by the police into locating his father, and then witnesses his father's death in a police shootout. After doing the final death rites of his father, he kills the person who was the cause of his father's death and escapes to Bombay.
Stranded and homeless in the big city, he is rescued by a kind-hearted Muslim fisherman who takes him to his home in the suburban slums Dharavi. His foster father is also a small-time smuggler known for his generosity in the slum. Upon his running afoul of a senior crime lord, the corrupt local police officer named Kelkar, arrests the fisherman on smuggling charges and subsequently murders him. Velu Nayakan, now a young man (Kamal Haasan) who has come into his own, goes in search of the officer and bludgeons him to death for revenge. As an act of remorse for his guilt, he decides to adopt Kelkar's mentally-challenged son Ajith, and raise him as his own.
With this act, he is seen as a saviour and a man to be feared amongst the slum residents. As their godfather and protector, he flourishes by resuming his late foster father's local smuggling activities. He marries a destitute school-girl-turned-prostitute Neela (Saranya Ponvannan) and has two children. Conflicts and power struggles occur in the smuggling world, in which Neela becomes a casualty. Velu's children are sent away to Chennai as a result and return some years later to their father's home, as young adults.
Velu's son Surya (Nizhalgal Ravi) is eager to join his father in his activities, despite his father's reluctance. For his first real test, he is required to eliminate a potential witness against his father; he does this by hiring outside thugs. They succeed in eliminating the witness, but their failure to cover their tracks leads police to him at a petrol bunk and an accident costs him his life. Velu is heartbroken. Velu's daughter (Karthika) is at odds with her father over his form of justice and killings, but Velu refuses to end his activities. As a last straw, she disowns him and leaves home.
Several years later, the newly appointed assistant police commissioner (Nassar) starts afresh to bring Velu Nayakan to justice over his alleged activities and manages to secure an arrest warrant. This commissioner is, unbeknownst to both, Velu's son-in-law. After a continued pursuit resulting in the thrashings by police and self-immolation of slum dwellers, Velu surrenders to the police to spare the lives of the residents of his slum. He is tried in court but is released due to the lack of adequate evidence. A supportive and emotional crowd gathers at the courthouse, awaiting his release. Velu is greeted by an excited crowd but their joy turns to sorrow when he is shot dead by a grown-up Ajith (Tinnu Anand), who has eventually learned the truth behind his biological father's murder.