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

Howard: A micro-valentine for a microbiologist.
Leonard: From her micro-husband.

Wolowitz: You love that spot.
Sheldon: No, I love my mother. My feelings for my spot are much greater. It is the singular location in space around which revolves my entire universe. And now it's yours.

TBBT Quotes

How those nipples feeling, chief?

Sheldon

Penny: Hey, Sheldon, did you change your Wi-Fi password again?
Sheldon: Yes, it's "Penny, get your own Wi-Fi." No spaces.