Priya Koothrappali is Raj 's younger sister. She first appeared in " The Irish Pub Formulation " and serves as the unintentional main antagonist of season 4 in that Penny regards Priya as Leonard 's most viable alternative girlfriend. Though she often looks annoyed or exasperated, she can be quite funny.
The American television sitcom The Big Bang Theory , created and executive produced by Chuck Lorre and Bill Prady , premiered on CBS on September 24, 2007.
Rajesh Ramayan " Raj " Koothrappali ,  Ph.D. is a fictional character on the CBS television series The Big Bang Theory , portrayed by British Indian actor Kunal Nayyar . Raj is based on a computer programmer that the show's co-creator, Bill Prady , knew back when he himself was a programmer.