Dr. Rajesh "Raj" Ramayan Koothrappali, Ph.D, is an astrophysicist and Howard Wolowitz's best friend. He often hangs out at Leonard and Sheldon's apartment, though he has his own apartment (the Raj Mahal) in Pasadena, California (the setting of the series). Raj fell in love with astronomy while attending Cambridge University. Originally from New Delhi, Raj has an Indian-English accent and, ironically, dislikes Indian food and culture. He frequently portrays himself as having come from humble origins and growing up in poverty in India, only for his friends to remind him that his father is a gynecologist, drives a Bentley, and has a house full of servants. For the first six seasons, his principal characteristic was a case of selective mutism social anxiety disorder, which did not allow him to talk to women outside of his family. This condition could be suppressed through alcohol (or if he thought he was drinking alcohol) or experimental social anxiety medications; however, the former usually ended up changing his personality, making him more obnoxious and overbearing, while the latter tended to have unpredictable side-effects.
By the ending of Season 7, Raj has overcome his mutism and can now properly talk to women without the need of alcohol or medication, though his love life continues. He frequently goes through different girlfriends but simply cannot find a long-term one.