Dr. Leonard Leakey[2] Hofstadter (Johnny Galecki) is an experimental physicist with an IQ of 173 who is originally from New Jersey and received his PhD at age 24, spending at least some of his time at Princeton University. He shares an apartment in Pasadena with colleague and friend Dr. Sheldon Cooper. Unlike his equally geeky friends, Leonard is interested and quite adept in building interpersonal and social relationships with others. Compared to his friends he is relatively successful with women. The writers have toyed with a romance between him and next-door neighbor Penny since the pilot, with their unresolved sexual tension being a major force for drama. Leonard dated Penny for most of Season 3, although they had dated briefly at the end of Season 1. Aside from Penny, Leonard has had romantic relationships with coworker Leslie Winkle, physician Stephanie Barnett, an unnamed French literature PhD, and North Korean spy Joyce Kim. Following his breakup with Penny, Leonard began a relationship with Raj's sister Priya in Season 4, and it is implied they had a brief sexual encounter before the start of the series on an occasion when Priya visited Raj. The two attempted a long-distance relationship after Priya moved back to India, but Leonard eventually broke up with her in Season 5 after she admitted to cheating on him with her former boyfriend. In Season 5's "The Beta Test Initiation", Leonard and Penny start dating anew though their relationship is rocky. Over the next two years they talk of marriage and each have unsuccessful proposals until the end of season seven when they become engaged. Leonard's family includes other accomplished scientists: his mother, Dr. Beverly Hofstadter, is a world-renowned psychiatrist, his sister is a biologist and his father an anthropologist. Also, his brother Michael is a Harvard law professor. It is mentioned in the season 2 episode "The Maternal Capacitance" that Leonard is the least successful member of his family. He is also known to be lactose intolerant and cannot process corn, as Sheldon states in "Pilot". Leonard also plays the cello. The cause of the elevator not working is also due in part to Leonard (and Sheldon) as the experimental rocket fuel he was developing was improperly mixed within their apartment and Sheldon threw the canister into the elevator shaft right before the explosion.