P.Sreekumar completed the screenplay of Karnan by researching and travelling through on Kurukshethra warfare lands of Haryana.He tells his dream story first to Actor Mohanlal.
Then how it goes to Mammotty ? Because mammootty loves to do the roles of ancient epics and characters to perform in movies. Why ? Mohanlal loves the script of the movie and agrees to do the film.Mammootty came to know about this and he also read the script of Karnan and he was impressed alot.Mammootty asked P.Sreekumar the role in Karnan.Mohanlal came to know that mammootty had loved the role and mohanlal drops the movie for mammootty.