Leonard is an experimental physicist from Caltech who rooms with Sheldon in their rundown apartment building in apartment 4A, in which the elevator always seems to be out of order. He keeps a whiteboard in their living room on which he works on theoretical particle physics. While Sheldon’s genius seems to be focused primarily in math and science, Leonard is indicated to be proficient in literature and history as well as the sciences; he is able to solve a woman’s crossword puzzle in seconds, the answers being mostly literature based, e.g. Vladimir Nabokov. It is also suggested that Leonard’s IQ is not as high as Sheldon’s; Sheldon scoffs at Leonard’s whiteboard theories as common enough to be “scribbled on the wall of every men’s room at MIT.” Most of the equations on Leonard and Sheldon’s boards feature complex higher mathematics, such as virtual particles in QM, or series of Reimann zeta functions. Leonard feels at home with his genius colleagues, but wants more socially. He is reluctant to let Penny know about his recreational activities (such as Klingon Boggle) and is probably reluctant to even partake in such activities in the first place, because although he secretly likes them, he doesn’t like to be seen as a nerd. He also dislikes his friends’ habit of rattling off different trivial facts, something to which all the other geniuses enjoy both listening and participating. Sweet but sarcastic, Leonard also seems to be the most well-adjusted one of the group; he is quick to try new things apart from his nerd friends and, between Sheldon and him, is the only one who feels that he “should do something” when Penny begins to recount her recent breakup. Despite his attempts to reject his nerd status, he certainly is one, with his Star Wars hygiene products and his ability to blurt out the wrong things in front of women, such as when he’s trying to invite Penny to lunch and mentions that curry is a natural laxative. He falls head over heels for Penny within seconds of spotting her and while at first it seems like lust rather than love, by the end of the pilot episode he has already announced to Sheldon, “our babies will be smart and beautiful.” Sheldon, however, is quick to add, “not to mention imaginary.”

Quick Facts

• Leonard wants to win a Nobel Prize someday (though Sheldon doubts he’ll ever achieve it).
• Leonard, as a physicist, is skeptical of string theory.
• Whilst Leonards IQ is never stated in a show, Sheldon states in the Pilot that Leonard and Sheldon have a combined IQ of 360.Sheldon states that his IQ is 187, so therefore Leonard must have an IQ of 173, though Sheldon also states his intellect can not be accurately measured by an IQ test, this may suggest that Leonard might have a higher IQ.
• Leonard received his PhD at the age of twenty four years old.
• Leonard has a grandmother with Alzheimer’s that came to Thanksgiving and stripped naked.
• Leonard wears boxer shorts.
• Leonard usually wears neutral colored sweat jackets.
• Leonard wears black framed glasses… even if in costume.
• Leonard cannot process corn and is lactose intolerant.
• Leonard has Darth Vader ‘No More Tears’ shampoo and Luke Skywalker Hair conditioner.
• Leonard is a huge Superman fan, so much so that he owns all of the Superman films and more than 2600 Superman comics.
• Leonard once dated a girl (presumably Korean) named Joyce Kim. He claims to have broken up with her, but Sheldon reveals that the end of their relationship was because she actually defected to North Korea.
• Leonard is commonly seen wearing “Geek Wear” (clothes that are scientifically inspired) such as, in episode 1×03 where he can be seen wearing a shirt with a “Paradox” molecule.
• Leonard and Sheldon own Dell XPS computers.
• Leonard can play the cello.
• Leonard’s middle name is Leakey (named for the famous anthropologist that his father worked with, “it had nothing to do with your bedwetting”).
• Leonard and all his friends play Halo 3 every Wednesday.
• Leonard and Sheldon are named after actor and producer Sheldon Leonard.^[1]
• Leonard has an iPhone.
• Leonard’s parents are presumably not comfortable with his choice of vocation.
• Leonard is unaccustomed to observing birthdays, by choice of his mother’s views on Psychiatry.
• Leonard’s parents live in New Jersey
• Leonard drives a silver car with a luggage rack on top.
• Leonard, if dumped, will go on a two week cycle of Emo songs and calling Sheldon down to pet stores to look at cats.
• Leonard owns a large collection of toys, games and memorabilia which has been nicknamed ‘nerdvana’.
• Leonard plays lead guitar on Rock Band.
• Leonard plays Age of Conan with the guys and is probably an Assassin.
• Leonard has sleep apnea.
• Leonard gets carsick unless he sits in the front, and even then it’s iffy.
• Leonard is currently dating Penny
• Leonard has trouble making eye contact, only being able to do so with Penny and the rest of his friends, which could be indicative of Asperger’s, ADD, or simply social anxiety.

Source: Big Bang Theory Wikipedia