Simon Helberg stars as Howard Wolowitz, the only one of the nerds that is not a doctor. He is an engineer at Caltech and is friends with Leonard and Sheldon and frequently is over at their apartment. Wolowitz mostly goes by his last name and still lives with his mother.
Most jokes with Wolowitz revolve around his failed attempts at womanizing, though he was given a girlfriend, Bernadette, in season three.
Howard: Creepy chummy, like you and your dog.
Raj: She feeds him out of her own mouth?
Howard: I mean, he calls her Debbie, she calls him Stewie and they're all giggly around each other. And believe me, when food goes in that mouth, it does not come out.
Howard: What do you want us to do about it?
Sheldon: You clearly weren't listening to my topic sentence: Get your women in line!