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 whispers in Wolowitz's ear]
Penny: What did he say?
Wolowitz: He compared Sheldon to a disposable feminine cleansing product one might use on a summer's eve.
Penny: Yeah, and the bag it came in

Sheldon: What are you doing now?
Howard: Making a straw.
Sheldon: Why?
Howard: So I can shoot you with a spitball.
Sheldon: You're not going to do that, and I'll tell you why. This is an institution of higher learning, I am your professor, and you're going to treat me with the prop... You shot your spit in my mouth!
Howard: Is that gonna be on the test? Because I don't think I could do that again.

TBBT Quotes

Later, Losers!

Raj

Okay, please don't take this the wrong way, but I'd rather swim butt-naked across the Ganges with a paper cut on my nipple and die a slow agonizing death from a viral infection than work with you

Raj [to Sheldon]