Dr. Rajesh Ramayan "Raj" 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. Raj fell in love with 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.
He is portrayed by Kunal Nayyar.
Raj is 5' 7" (1.70 m), with warm tan skin, black hair and brown eyes. He is normally seen wearing a layered combination of a shirt, a sweater vest, and a windbreaker with cargo pants and skate shoes; he wore a red baseball cap in the Pilot.
Rajesh Koothrappali was born in New Delhi, India on October 6, 1981 to Dr. V.M. Koothrappali and Mrs. Koothrappali. He also has a younger sister Priya and also 3 brothers and 1 other sister. While growing up in India, he didn't really like it there and grew to dislike his country's food and culture. Later, Raj left India and moved to Pasadena, California in the United States of America. There, he met Howard Wolowitz who became his best friend and Howard's mother made Raj feel welcome into their house.(Although she thought he was the gardner for two years)
However, in "The Grasshopper Experiment" everyone discovers that Raj can actually talk to a woman by being drunk, as evidenced when Penny gives him a cocktail while going through bar tending training.
In "The Porkchop Indeterminacy", Raj takes some drugs as another way to talk to women. When Sheldon's twin sister Missy Cooper comes for a visit, Raj, Howard and Leonard begin to clash over who is going out with her and the three engage in a fight. Raj was the third person to ask Missy out, but his drugs wear off and leaves defeated.
In "The Griffin Equivalency", Raj gets some glory after being featured in People Magazine, when the guys fail to take interest, Raj angrily leaves Leonard and Sheldon's apartment. The next day, The guys apologies and invite him out for dinner, before Gablehauser congratulates Raj for his work an invites him for lunch in the president's dinner room. Raj brags about his work to the guys and invites Penny to People's reception. After the party, Raj talks to his parents, but leaves to throw up. Raj tries to give Penny an apology note but Penny forces him to verbally apologies, who does so and Penny forgives him.
In "The Pirate Solution" Raj's work hits a dead end, causing him to have concerns of being deported back to India, he begins working for Sheldon in order to keep his visa valid. He also become jealous when Leonard and Howard become too busy with their girlfriends to hang out.
In "The Hot Troll Deviation" Raj buys a desk bigger that Sheldon's and the two fight over in the office (in the later episodes, Raj and Sheldon have gotten along with each other and made amends).
In The Irish Pub Formulation" Raj becomes furious when Leonard starts a relationship with his sister while she's in town.
In "The Roommate Transmogrification", Raj and Penny become closer friends, up to the point where they allegedly have a one-night stand.
In "The Countdown Reflection" Raj suggests that they do Howard and Bernadette's wedding on the roof since he knows that as an astrophysicist that there is a satellite above Pasadena, so it can photograph the ceremony from space.
In "The Tangible Affection Proof", Raj begins a relationship with a woman called Lucy, but in "The Monster Isolation", Raj becomes a hermit when Lucy dumps him on their date, until Howard brings him back to his senses.
In "The Bon Voyage Reaction". Lucy breaks up with him when he pushes her to meet his friends. When Penny visits a miserable Raj, he gets over his selective mutism and is now finally able to talk to all women.
Raj begins a relationship with a dermatologist, Emily Sweeney.
In "The Expedition Approximation", Raj continues to work with Sheldon on Dark Matter testing, when both Sheldon and Raj go down the very hot mines of the university for an expedition, Sheldon cowardly leaves Raj at the mercy of rats after spending 11 minutes down there.
He then starts to question his relationship with Emily, wondering if she really is the right person for him.
In "The Valentino Submergence", he breaks up with Emily so that he can date Claire. But in "The Application Deterioration", he and Emily have gotten back together, as seen in the last scene of the episode, when they are both lying in her bed.
Raj meets a screenwriter and bartender named Claire, and gets involved in a love triangle with her and Emily.
Raj is no longer in a relationship, though he finds an interest in his workplace's cleaning lady, Isabella.
Raj has been good friends with Howard since he first moved to the United States. For the fifteen years that followed, Howard has teased and joked around with Raj most of the time. In The Confidence Erosion (S11E10), Raj's father expresses his beliefs that his son's lack of confidence is because of Howard's teasing, leading to Raj cutting off contact with Howard, much to the latter's chagrin. However, they become friends again in the next episode, The Celebration Reverberation (S11E11), while taking out their frustrations on each other.
- Raj's selective mutism even applies in his dreams, the notable nightmare he had is with Siri as shown in "The Beta Test Initiation".
- He has a Ph.D. in Astrophysics.
- The baseball cap Raj wears in the Pilot bears the number 42 (the answer to life, the universe, and everything) on it.
- Raj is 5 ft. 7 in (1.70 m) tall – the height of his actor Kunal Nayyar. This measurement is two-and-a-half inches below the average height for males in the U.S. and two inches above the average height for males in India. In "The Transporter Malfunction", he states that, next to Howard and Bernadette, he looks 6 ft. 2 in (1.88 m) tall.
- Like Sheldon, Amy, Bernadette, Leonard, and Leslie Winkle, Raj lives in an apartment, which he calls his "Raj Mahal".
- Raj is not at all serious about his Hindu faith and eats beef, which is frowned upon by most Hindus.
- Raj calls his skin tone "Melt-In-Your-Mouth Caramel".
- Raj, much like Howard, despises many of Sheldon's antics, and the two managed to get Sheldon on a date with Amy Farrah Fowler on a dating website in "The Lunar Excitation", much to Sheldon's dismay.
- Raj's case of selective mutism was first evident in the Pilot episode.
- Raj's selective mutism does not apply to his female family members such as his mother and his sister Priya Koothrappali.
- Raj dislikes Aquaman, and he is always chosen to dress as Aquaman, due to the guys having a costume competition.