When asked about the Bachchan presence in the film, director Milan Luthria says, "I don't know where you heard this. But it's true. In the course of the film Ajay's character's girlfriend played by Kangana Ranaut mentions to him that there should be a film made on his life. To this Ajay replies, 'Now you want me to turn into an actor?' Kangana then tells Ajay about this young intense actor named 'Ami' who is just right to play Haji Mastan."
The Big B had played Haji Mastan in Yash Chopra's Deewaar which was released in 1975. Once Upon A Time In Mumbai is set in the 1970s. Interestingly Devgn, who plays Mastan in Milan Luthria's film was often compared to the Big B when he started his career, even by Jaya Bachchan.
Luthria says the Big B is not mentioned by name. Says the director, "I'd never make any reference to Mr. Bachchan that can be considered even remotely disrespectful. But yes, Kangana refers to him as 'the young intense actor'.
Besides the fact that they both play characters inspired by the same real-life character, the interesting part of the Bachchan reference in Devgn's context is that the younger actor has perpetually been compared with the Big B's for the dark and brooding intensity.
In fact, Jaya Bachchan had long ago singled out Devgn as the successor to her husband.