He has taken colours from movies like 'Deewar' and 'Zanjeer' to recreate a retro look with contemporary coating for "Once Upon A Time In Mumbaai". Director Milan Luthria says it is only a fictional take on the underworld dons of the 1970s and not a biopic on any particular individual.

"The movie is not in essence a true biopic of anybody. It is not specifically based on any one person. There is a lot of media speculation, " Luthria told in a telephonic interview from Mumbai.

"To say that it is a true portrayal of any character would be wrong because that would be doing injustice to the individuals. If it was to be a biopic, then I would have been completely true to the fact and when I am not, it would be an insult to call it a biopic. It is not a hardcore biopic on any individual."

Set primarily in the 1970s Mumbai, the film will trace the changing face of the underworld through the eyes of a police officer. The story follows the rise of Sultan (Ajay Devgn), and his eventual fall when his protege Shoaib (Emraan Hashmi) challenges his supremacy and usurps power to rule the underworld in the city.

Produced by Balaji Telefilms, the film is releasing July 30 and the cast also features Kangana Ranaut and Prachi Desai.

"We have a completely fictional and filmy take on the gangsters and smugglers that were around in the 1970s. I have just taken colours from wherever I wanted and it has influences from movies like 'Deewar' and 'Zanjeer' that I saw as a child, " he said.

"It is essentially about the time when the first organised crime happened in Bombay and when the mafia was born. It starts from there and goes to the first challenger to the original godfather, " said Luthria, who has made films like "Kachche Dhaage", "Chori Chori" and "Taxi No. 9 2 11".

"It was fun to go back to the age of those cars, cabaret, smugglers, drama, one-liners and fast-paced movies. But it is not a hardboiled mafia film in that sense. It is an early 1970s drama told in a very contemporary visual style, " he added.

Digging out the information of yesteryear goons was a tough task for the director.

"As far as people of that time are concerned, especially smugglers or gangsters, unfortunately there is not much rich material available on them."

Recreating the retro look for the movie wasn't easy either.

"There is a strong emphasis on the look and the locations in the film which was very difficult. The styling was done after extensive research. The colours, lightings and accessories are all a large part of the film's canvas. So we had to be accurate about what cars we were using to what kind of number plates to be used, " he said.

In the last three decades, the city has changed manifold and scouting locations to shoot the film was again a mammoth task. The major change that the city has witnessed is its name - from Bombay to Mumbai.

"Finding areas of Bombay still untouched by the changing times was difficult. It was primarily south Bombay that we could capture and large parts of the dock areas like Darukhana, Dongri, dockyard and the mills area where no films have been shot before, " said Luthria.

"We had a very difficult time to go and shoot there as these are very difficult areas to access - roads are narrow, streets are overcrowded, people not used to seeing movie stars, so a lot of cars were damaged and a lot of fights broke out.

"We had to draw maps and explain to the actors how to reach various points. We had to quadruple our security but at the end of the day we got what we wanted, " he added.