I saw Nagayan Hindi dubbed version, and now I can make a comparison between the two. I also recommend that you see this excellent Hindi dubbed version of Nayagan before you watch Dayavan.
The main comparsion between the two films is that Nagayan is a more-to the-point film, whereas Dayavan like all Bollywood films has masala (spices) added to it to make it more appealing.
If you ask me frankly, I would say that Nayagan is a better film in all respects and brilliantly acted and directed as well. I should advise you to see and own both Nagayan and Dayavan.(Everyone is entitled to his/hers own opinion.)
Changes: the role which Kamal Hassan played as the main figure is now replaced by the excellent veteran actor Vinod Khana. This is one of his most famous roles. The film also stars the actor and director of the film, the late Bollywood Legend Feroz Khan whose loss is still deeply felt to me.
Feroz Khan's career in Bollywood is legendary and his movies are all blockbusters. I like his style of direction and the way he introduces characters in the film. This film is also one of his biggest contributions to Bollywood.
Maduri Dixit is stunning as always. And her acting is on a different level altogether. She still is the best actress in Bollywood and the pace-setter.
The songs in the film are the highlight. "Aaj phir tum pe pyar aaya hai..." is my personal favorite. This song is sung by the Legendary Pankaj Udhas.
Plot: After having witnessed the tragic death of his father by the local South Indian police, and being orphaned and homeless, Shakti Velhu develops a hate, and distrust of the police in India. He is befriended by another homeless boy named Shanker, who asks him to accompany him to Bombay's slumlands, where they live with a kind-hearted Muslim named Karim Baba, and his daughter, Shama. This is where Shakti and Shankar spend their childhood. When they mature, they take to petty crime. Here too, Shakti witnesses police brutality and atrocities, especially at the hands of Police Inspector Ratan Singh. When Karim Baba is arrested, jailed, and found dead in police custody, Shakti hunts down Ratan Singh.
An investigation is launched, but no one comes forward as a witness. Thus Shakti gets his reputation as a Don with a good heart viz. Dayavan.
Shakti marries Neelu, and has two children, Suraj and Sarita. He becomes even more powerful and influential all over Bombay, and his working partners are powerful criminal dons who have ruled over Bombay for eons. Shakti eventually replaces these dons, and becomes Bombay's only Don. This creates enemies for him and his family, but he believes since he has not really done any harm to anyone, he and his family will be safe. It is this belief that will take a heavy toll on his life and that of his family.
Full 10/10: a must have film for all Hindi film lovers, and Feroz Khan and Vinod Khanna fans.
