Penny

Penny is the one main character on The Big Bang Theory that doesn't have an advanced degree.  Perhaps not coincidentally, she is the most socially adept of all the main characters, with the possible exception of Priya.  It's funny, in that despite the fact she is the 'least educated' of the characters, she is often looked up to by the likes of Amy Farrah Fowler and Bernadette, at least when it comes to certain non-science-y topics.

So far, I believe she has spent the entire series working at the Cheesecake Factory and auditioning for acting jobs.  She has the Chinese character for soup tattooed on her right buttock.

She is or has been the object of Leonard's, Raj's, and Howard's desires, for obvious reasons. 

Penny is from Nebraska.

(Penny is played by Kaley Cuoco.)