<Tr> <Td> Ruchi </Td> <Td> Swati Kapila </Td> <Td_colspan="10"> </Td> <Td> Recurring </Td> </Tr> <P> Leonard Leakey Hofstadter (Johnny Galecki) is an experimental physicist with an IQ of 173 . Originally from New Jersey, he received his PhD at age 24, spending at least some of his time at Princeton University . He shared an apartment in Pasadena with colleague and friend Dr. Sheldon Cooper until season 9 . Unlike his equally geeky friends, Leonard is interested and quite adept in building interpersonal and social relationships with other people . Compared to his friends, he is relatively successful with women . </P> <P> The writers have toyed with a romance between him and next - door neighbor Penny since the series premiere, with their unresolved sexual tension being a major force for drama . Leonard dated Penny for most of season three, although they had dated briefly at the end of season one . Aside from Penny, Leonard has had romantic relationships with co-worker Leslie Winkle, physician Stephanie Barnett, an unnamed French literature PhD, and North Korean spy Joyce Kim . Following his break - up with Penny, Leonard began a relationship with Raj's sister Priya in season four, and it is implied they had a brief sexual encounter before the start of the series . The two attempted a long - distance relationship after Priya moved back to India, but Leonard eventually broke up with her in season five after she admitted to cheating on him with her former boyfriend . In season five's "The Recombination Hypothesis", Leonard and Penny start dating anew, and although their relationship is initially rocky and Penny has doubts, in season six, she works through her doubts and has a stronger relationship with Leonard . </P> <P> In season six's "The 43 Peculiarity", she tells him she loves him for the first time, and this now makes them more comfortable in their relationship . Over the next two years, they talk about marriage and each have unsuccessful proposals until the penultimate episode of season seven, when they become engaged, and finally get married in the ninth - season premiere, followed with a wedding redo for their friends and families since the couple had eloped . In season, after Sheldon moves in with Amy, Leonard and Penny have apartment 4A to themselves . Leonard's family includes other accomplished scientists: his mother, Dr. Beverly Hofstadter, is a neuroscientist and world - renowned psychiatrist, his sister is a medical researcher, and his father, Dr. Alfred Hofstadter, is an anthropologist . Also, his brother Michael is a Harvard law professor . He is known to be lactose intolerant, and is also known for playing the cello . </P>

Who plays leonard's girlfriend on the big bang theory
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