 The producer Nariman Irani was a cameraman who was in deep debt of  around Rs 12 lakhs ( a lot of money for that time) after his first  film Zindagi Zindagi with Sunil Dutt that flopped miserably. So to  get out of this financial mess he was advised by Amitabh Bachchan,  Zeenat Aman, Chandra Barot and Manoj Kumar to make another film  which subsequently turned out to be Don. Writers Salim