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

Wolowitz: Oh, more details about the new Star Trek film. There's going to be a scene depicting Spock's birth.
Raj: I'd be more interested in a scene depicting Spock's conception.
Sheldon: Oh, please. For Vulcans, mating—or if you will, pon farr—it's an extremely private matter.
Leonard: Still, I'd like to know the details. His mother was human; his father was Vulcan. They couldn't just conceive.
Wolowitz: Maybe they had to go to a clinic. Can you imagine Spock's dad in a little room with a copy of Pointy Ears and Shapely Rears?

Howard: Should we stop holding hands now?
Sheldon: In a minute.
Howard: Okay, good.

TBBT Quotes

(Singing) Thor and Dr Jones, Thor and Dr. Jones. One plays with lightening, the other plays with bones.

Howard and Raj

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