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: Hey, I work at the same university you do.
Sheldon: Yes, and Hawkeye's in the Avengers but no one ever says, "Help, Hawkeye!"

Sheldon: Won't that void the warranty?
Howard: Sheldon, I have a masters degree in engineering. I wipe my bottom with warranties. Except for Apple Care. That pays for itself in the long run.

TBBT Quotes

You can't ruin a friendship with sex that's like trying to ruin ice cream with chocolate sprinkles.

Raj

Sheldon: Even the dung beetle chooses to plot its course by using the Milky Way.
Raj: Is that true?
Sheldon: Everything I say is true. Now, of course, the dung beetle also enjoys eating fece, living in feces and making little balls out of feces. So, pick and choose which aspects of its lifestyle you want to embrace.