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-Javed were not able to sell the script for a long time until director Chandra Barot and producer Nariman Irani bought it. It was rejected by Dev Anand, Prakash Mehra and Jeetendra. The script did not even have a name. It was a script pertaining to a character called Don. When Nariman Irani approached Salim, he said, 'Humare paas ek breakfast script padi hai jo koi nahi le raha hai.' And Nariman said 'chalega'. So that is how Don was made.
At the beginning of the film when Iftekhar, who plays DSP De Silva, saying names of the fictional smugglers, he mentions Haribhai Zariwala, which was the real name of late actor Sanjeev Kumar.
The song "Khaike Paan Banaraswala" was originally written for the Dev Anand movie Banarasi Babu (1973), and was never meant to be in this film. It was shot after filming was complete and was added after the intermission to balance the action-packed pace of the movie.
Amitabh's look was inspired from a character played by Sanjeev Kumar in his film Naya Din Nayi Raat. Sanjeev plays 9 characters in the film and one of them is the role of a masterji where he eats paan and has oily hair.
During a car chase scene, Mac Mohan played a prank on Amitabh Bachchan and drove his car so fast that Bachchan got scared. He got his own back later by mixing Mohan's drink with alcohol during one of the songs - he was drunk on set.