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.