Amitabh received tremendous flak initially for his voice but the role remains one of his most memorable characters, till today Amitabh is mostly imitated by his act in this film.
To give Amitabh Bachchan the gangster look, his mouth was stuffed with cotton wool underneath both cheeks, as was Marlon Brando's in The Godfather (1972)
Mithun Chakraborty's unique role of Kishnan Iyer was inspired by one of his room mates of his struggling days, before he become a popular film star. In his struggling days Mithun used to be be room sharing with Devio who used to pay rs 150 while Mithun Used to pay rs 75. Devio had the a bed while Mithun used to sleep on the floor, one specific time Mithun used his bed whilst he was at work and when Devio came back he scolded Mithun. This incident remained with Mithun and he put Devio's character on screen.
The song Jhumma Chumma De De was actually planned for this film but the director felt it would not go with Amitabh's role and hence the song was replaced by Ali Baba and Jhumma Chumma was used in HUM.
Though Deepak Shirke, Avtar Gill, Danny are older in the film then Bachchan, in reality all are either of same age to him or are younger.
Amitabh Bachchan's mother played by Rohini is actually much younger to him in real life.