What would it be like to see ‘Sholay’ and ‘Znjeer’ without Amitabh Bachchan? It is really hard to imagine anyone else as Jai in ‘Sholay’ apart from Mr. Bachchan similarly no one can take the brooding image that he constructed of Jai in ‘Zanjeer’. But had the makers had their way things would have been totally different.
Prior to ‘Zanjeer’ as a hero Amitabh Bachchan didn’t had a single hit film but it was with ‘Zanjeer’ that changed and the Hindi film industry got the ‘angry you g man’ a cult image that had been revered  abd emulated till date. So who was to be Vijay in Prakash Mehra’s ‘Zanjeer’ instead of Amitabh Bachchan? It was Raaj Kumar. But the actor refused to work with Mehra and the film went to Bachchan’s kitty and the rest was history.
Similarly Amitabh Bachchan was not considered for the role of Jai in ‘Sholay’. Shatrughan Sinha was envisioned for the role of Jai but thanks to Dharmendra, that Amitabh Bachchan got the part. Dharmendra was able to convince Ramesh Sippy to take Big B onboard for the role.
It is difficult to imagine anyone else in these roles other than Big Bi, it seems they were tailor made for him and anyone else would have failed to do the justice. Just try to recreate the image of someone else apart from Amitabh Bachchan as Jai or Vijay and see if you can come up with it.