Iruttinte Athmavu (transl. The soul of Darkness) is a 1967 Indian Malayalam-language film directed by P. Bhaskaran and written by M. T. Vasudevan Nair based on his own short story of the same name. It stars Prem Nazir and Sharada in lead roles with Thikkurissy Sukumaran Nair, P. J. Antony, Ushakumari, Kozhikode Shantha Devi and Baby Rajani in supporting roles. The film is about a mentally unstable youth born into a matriarchal family who is forced to live as a mad man in chains and who is misunderstood and ill-treated by everyone except his uncle's daughter. The film features music by M. S. Baburaj, cinematography by E. N. Balakrishnan and editing by G. Venkitaraman and Das.

Prem Nazir played the mentally challenged Bhranthan Velayudhan, widely considered to be one of the finest performances of Prem Nazir's career. Nazir himself rated his role of Velayudhan in Iruttinte Athmavu and as the swashbuckling folk hero Thampan in Padayottam as his best. Also, its script is regarded as one of the finest by M. T. Vasudevan Nair. A landmark film in Malayalam cinema, the film provided Malayalam cinema with a new direction; that of the low-budget film. The film has earned a dedicated cult following. It won the National Film Award for Best Film on Other Social Issues. It missed the Best Film and Best Actor (Prem Nazir) award only narrowly. Despite all the acclaim, the film was a box office failure.

The film was part of MT's trilogy of political melodramas – the other two being Murappennu (1965) and Asuravithu (1968), both directed by A. Vincent. Major indoor parts of the film were shot in Satya Studios in Madras and outdoor parts from the premises of Bharathapuzha at Shoranur.