The film, which is inspired by murdered theatre activist Safdar Hashmi, also stars Ajay Devgan and Vidya Balan.
Talking about his character, Pankaj said: "Well, this man has not been the best of people and goes to jail. In the prison he sees this rehabilitation operation going on and decides to get involved. In the process he gets reformed. When he is released, he tries to work towards what could stop his fellow people from turning into a bad person. And he takes up street theatre to spread his message."
That sounds like the story of Valmiki, who authored great Indian epic "Ramayana".
"No. I did not have anything of that sort in my mind. I played out the role of Sidhu from my imagination. I don't know if there was any such perception in the director's mind. I was not informed of it if there was," the veteran actor told.
"I look at it from a different point of view. I see the character as an artist who wishes to uplift people and want to do something good for them, but he has a past, which is not quite good."
To make his character authentic in "Halla Bol", Pankaj grew beard and kept it till the shooting continued.
"As an actor, I am not comfortable with an artificial beard. The character had to look authentic and real and a little menacing. So I grew the beard."
Panakj says he chose to play a reformed dacoit because it offered him to explore different avenues as an actor.
"I thought it was very different and as an actor I would get to explore something I hadn't done before. Hence, I went in for the film on the narration."
His last film "Dharm" too saw him playing a person who is reformed and a reformer. Pankaj calls it a coincidence.
"It's not a conscious decision. I have always taken up films that I like. And in the process if I have done films, which bring out something that could do society good I think it's great. It is always a responsibility on us that we should do something for a good cause. As an artist if I am able to do it, I would surely do it."
The actor, who has done some very thought provoking films, says he gives importance to three things while selecting a film.
"First, the content; second is the script, and third the director. It's very important that the director is capable of doing a good work out of the whole story. The director needs to have a vision and clarity in his mind. It's not enough to know the story, he or she should have the knowledge and efficiency to execute it articulately.
"Also the story is extremely important. Small events and some songs and dance do not make a film. A film needs to have a proper structure and there has to be an output which would be relevant to people who watch it."
Though this is Pankaj's first film with Santoshi as a director, they know each other for a long time.
"Yes, this is the first time I have worked with him. But we have worked together when he was chief assistant director to Govind Nihalani. Even then we believed that he had great potential. And he has proved us right. Look at his body of work. He has done almost everything and done really well.
He is equally thrilled working with Ajay and Vidya. "They are good actors and it's been a nice experience working together. I really enjoyed working in 'Halla Bol'."
Asked what he enjoys most - TV, films or theatre, he said: "Nothing like that. I don't have preferences, but then TV has become very limited for me. We all know that it's saas-bahu sagas. I don't quite identify with these. Theatre of course gives you a different kind of kick as the feedback comes immediately."