Nawazuddin Siddiqui has played supporting roles in a number of films that I did not notice him. Like many I tend to focus on the leading characters, but have come to realize if we don't accept the supporting actors as believable characters, the romance, the mystery, the suspense, the excitement is greatly diminished. The fact that we enjoyed or at least appreciated a movie is a credit not only to the (celebrity) leading actors, but to the whole ensemble. Nawazuddin has worked hard in many small roles and has been given the opportunities to demonstrate his versatility and believability in more significant roles.
First time noticed was in "Kahaani," truly a great film with a super twist ending. He played a very despicable character who basically admitted that he was as much a scoundrel as the bad guys, but it was ok because he was the law. The viewer is disgusted. He made Vidya Balan more creditable as a heroine and the movie more suspenseful than it would have been otherwise.
Second film I noticed was in "The Lunchbox" a film festival favourite. His role was obsequious, trying to please everyone. Again he is playing the third character, but gives a sounding board and a contrast with Irrfan Khan. A hit at the Toronto International Film Festival.
"Gangs of Wassepur," released in 2012 was a 5 hour blockbuster that is often called the Bollywood equivalent of "The Godfather." To me there was too much senseless killing done very casually (more than with the Marlon Brando version) On the other hand they explained different methods of corruption that gangsters took part in to make money. Nawazuddin played a very cold blooded killer with a few human moments. Directed by Anurag Kashyup.
In "Talaash" released in 2013 he played a bad guy with a bit of a heart. He truly loves a prostitute who has been abused. Aamir Khan starred, always a mark of quality, especially in details. Buried in the credits.
2015 was a big year for Nawazuddin releases. "Badlipur" saw him as another bad guy. Involved in robbery where Yami Gautam was killed. It boils down to an unusual revenge story very well done where in reality Nawazuddin is the main focus, but also noteworthy were Varun Dhawan and Radikha Apte.
In "Bajrangi Bhajga" with Salman Khan he played a journalist who saved the day for the hero in a very popular and critically successful film. Salman Khan for the most part drops his macho persona and plays a simple man trying to help a young mute girl back to the fearful Pakistan. Siddiqui appearing in second half comes through as a Pakistanni journalist who at first writes against Salman, but soon becomes a supporter and is key to the happy ending of the movie.
In "Manjhi: The Mountain Man" he goes one step beyond to become the leading hero, based on a true hero who over 22 years working with hammer and chisel mostly alone to create a path through a mountain. His wife (whose death inspired the effort) was played by Radhika Apte, the two of which were a really good match to watch. She doesn't disappear after her death.
He is very good at projecting a happy go lucky image or a deadly killer. But more than that he immerses himself in the character so you stop thinking of him as a mere actor and enjoy (or hate) the character and how it fits into the story. He adds to every film.