Originally Satish Kaushik was supposed to play the role of Nandu.Nandu's really cartoonish appearance in the film was something Satish Kaushik was not ready for. Roop ki Rani Chiron Ka Raja was flopped just recently and Kaushik was really depressed. He told David Dhawan that if he will do Nandu, people may think he has given up after the debacle of RKRCKR. David understood him being an old friend and made a switch. Shakti Kapoor was doing Muthu's role in Sajan Chale Sasural. So he gave that role to Kaushik and casted Shakti Kapoor in Raja Babu. Both actors won the best supporting actor film fare award for their respective roles.
It is said Govinda improvised most of the lines he had with Shakti kapoor, "samajhta nahin yaar" and "nandu sabka bandhu" were lines created by Govinda.
Shakti Kapoor won the best comedian Filmfare award.His only award till date.
In 1982 film Namak Halal Shashi Kapoor's character was called Raja Babu.
Dialogue's like Nandu Sambka Bandhu and Samajta Nahi Hai Yaar were developed by Govinda on the sets.They were never part of the script.