Dr. Leonard Hofstadter, a physicist at Caltech, got his PhD at the age of 24 thanks to his 173 IQ. Leonard lives with his best friend and co-worker Sheldon.
Leonard is definitely the most social of his nerd group of friends and has a crush on their neighbor, Penny. Leonard went on a date wih Penny at the end of season one, but it didn't work out due to their insecurities.
During the third season of Big Bang, Leonard returned from his artic expedition with the guys and began dating Penny.
Sheldon: I have got the Sword of Azeroth!
Leonard: Forget the sword, Sheldon. Help Raj.
Sheldon: There is no more Sheldon. I am the sword master!
Wolowitz: Leonard, look out!
Leonard: Damn it, Sheldon, we're dying here.
Sheldon: Goodbye, peasants.
Leonard: Bastard teleported!
Raj: He's selling the Sword of Azeroth on eBay.
Leonard: You betrayed us for money? Who are you?
Sheldon: I'm a rogue night elf. Don't you people read character descriptions? Wait, wait, wait... somebody just clicked Buy It Now.
Wolowitz: I am the sword master!
Wolowitz: So, how'd it go with Leslie?
Leonard: Oh, we tried kissing, but the earth didn't move... I mean any more than the 383 miles it was gonna move anyway