Jack and Jill are the two nasty and manipulative outlaws united in a life of crime. They are both diabolical, brutish, mean and violent. However, Jack seems to have a more loyal, sensitive and trustworthy side: Throughout the film, he suggests to Jill that they settle down and raise a child together, such as his favorite piglet named Hamhock. However, Jill is completely against the idea, preferring the criminal life instead. They also appear to be traitorous and greedy in nature.
Jack and Jill are in the possession of the magic beans from the Jack and the Beanstalk story. Eventually, Puss, Kitty Softpaws, and Humpty Dumpty track them down in their piglet-filled cart and, after battling them, manage to steal to get into the giant's keep.
However, it is later revealed that Jack and Jill were in cahoots with Humpty and Kitty to take the Golden Goose and trick Puss into being imprisoned in his home town. Jack and Jill were seemingly just Humpty's minions. Later on, the Great Terror arrives to retrieve the Golden Goose, its baby. It is revealed that Jack and Jill were planning to betray Humpty all along, wanting more than just golden eggs but the actual goose. They try to steal the Goose when Humpty had a change of heart and tried to help Puss lure the Great Terror away from San Ricardo, holding their gun to Humpty's head, only for Kitty Softpaws to fight them off and then be stomped on by the Terror.
During the credits, Jack and Jill are seen in full body casts. It is most likely that they will be sent to jail to pay for their crimes, once they've recovered from their injuries.
Jack's defeat in the credits.
Jill's defeat in the credits.
Throughout the film, Jack tries convincing Jill that they should have a family but she assumes that they should be taking care of their piglets.
Amy Sedaris, Jill's voice actress, previously provided the voice of Cinderella in Shrek the Third.
David Koechner was considered for the role of Jack before Billy Bob Thornton was cast.
Melissa McCarthy was considered for the role of Jill before Amy Sedaris was cast.
In their eponymous nursery rhyme, they were siblings. In the movie though, they are husband and wife.
At one point, Jill states the events of the nursery rhyme where Jack got a head injury.
Throughout most of the film, Jack keeps the magic beans in a box clamped around his left hand so that nobody can steal it from him.
They appear to be very good with technology as their cart has many impressive contraptions.