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

Look, Leonard. There's a bridge. Drive off it.

Howard

Howard: Wait. Wait. If it wasn't for Indiana Jones, the ark would never have ended up at the warehouse!
Sheldon: (gasps) That's true! He collected and delivered the ark to the proper authorities for filing.
Raj: Like a hero.
All: Yeah! Right! Yes!
Leonard: Although, technically, Indy was supposed to take the ark to a museum to be studied. He couldn't even get that done.
All: Aww.

TBBT Quotes

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

Leonard: Hi. I'm Leonard. You are beautiful. You pop, sparkle and buzz electric. I'm going to pick you up at eight, show you a night you will never forget.
Raj: Where are we going?