Debra Morgan is Dexter's step-sister.
They became related when Dexter was adopted by Deb's father, Harry, who instantly developed a bond with his new son. Deb grew of very jealous of it.
Debra is a detective in the Miami Police Department. At one point, she got engaged to a man that ended up being the notorious murderer known as The Ice Truck Killer. That's never fun.
This detective as a seriously dirty mouth and a very aggressive, up-front attitude. She's far from shy.
Debra Morgan: Why is it we never talk brother-sister stuff?
Dexter Morgan: Our dad was a cop, you're a cop, I work for the cops... for us, this is brother-sister stuff.
Dexter Morgan: So what's up, hot shot?
Debra Morgan: Alright, get this. Lieutenant's looking for that refrigerated truck in every swamp, glade and chop shop from here to the Keys. The way I see it, that whack-job truck driver threw a severed head at your car. It's not as if he's shy.
Dexter Morgan: You think he's hiding the truck in plain sight, wanting it to be found?