Piper Chapman
Ten years before she landed in prison, Piper helped her then-girlfriend, Alex Vause, smuggle drug money during an extended vacation in Europe.
Alex Vause
Alex used to be a smuggler for a major drug cartel. Though she loved Piper, she also used her as a pawn in her smuggling operation. Ten years after the crime, Alex named Piper as an accomplice, and the two both end up at Litchfield.
Galina "Red" Reznikov
It's not completely clear what exactly lands Red in prison, but we do know that she and her husband owned a restaurant and that Red became involved with the Russian mafia. She punched one of the mob wives in the boob and ruptured an implant, but her solid business advice to the husband allowed her to stick around.
In season four, we find out that Red had several heads in her freezer at the time of her arrest.
Lorna Morello
While we first assume Morello is planning her wedding to her fiancé, Christopher, it's revealed that Christopher is the man she was stalking. After meeting at a post office, they went on one date, and she proceeded to stalk him. Eventually, she planted an explosive device in his actual girlfriend's car, attempting to murder her.
Tasha "Taystee" Jefferson
So far we just know that Taystee was involved in a drug ring run by Vee.
Nicky Nichols
Nicky is a former heroin addict who was raised by a wealthy but mostly absent mother. She was arrested for stealing a taxi with her friends so that she can get to her dealer in time to get drugs for the weekend.
Gloria Mendoza
On season two, we learn that Gloria has a complicated background with domestic abuse and was arrested for food-stamp fraud.
Carrie "Big Boo" Black
Though we've seen flashbacks of Big Boo as a child, the precise nature of her crime is unknown. We do know she ran a gambling ring and she refers to herself as a "thieving dyke" on season three, so it may have something to do with stealing.
