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 Wolowitz Quotes

Raj: I know. Being an astrophysicist right now is like being a rock star.
Howard: Only without the sex.
Raj: Yeah, literally, none of it.

Howard: Why don't you put her in a kennel?
Raj: Why don't you put your mother in a home?
Howard: To be honest, she'd do better in the kennel.

TBBT Quotes

Stephen Hawking: You made an arithmetic mistake on page two. It was quite a boner.
Sheldon: No, no ... that can't be right. I-I don't make arithmetic mistakes.
Stephen Hawking: Are you saying I do?
Sheldon: Oh, no, no, no, of course not. It's just, I was thinking.... Oh, gosh, golly, I made a boo-boo and I gave it to Stephen Hawking.
Stephen Hawking: Great, another fainter.

Sheldon: Why do you have the Chinese character for "soup" tattooed on your right buttock?
Penny: It's not "soup," it's "courage."
Sheldon: No it isn't. But I suppose it does take courage to demonstrate that kind of commitment to soup.
Penny: How'd you see it? You said you wouldn't look.
Sheldon: Sorry. As I told you, the hero always peeks.