Corruption
Gotham City is a place known for its criminal underworld. Bosses run all facets of society in the city by bribery, extortion and strong-arming. Carl Grissom is the main boss with all of the power in Gotham, but when he betrays his number one man, Jack Napier and doesn't finish the job he creates a new brand of criminal in The Joker. The Joker makes the corrupt bosses look like children compared to his wild and unpredictable nature as he not only corrupts the mob, but corrupts the resources of Gotham with chemicals to ensure everyone is afraid of the everyday items they use could kill them.
Revenge
As a young boy Bruce Wayne witnessed Jack Napier killed his parents in cold blood. Since that day Bruce has desired to take down Napier and this revenge has grown deeply inside of him. Thus, when Napier reappears as The Joker, Batman will stop at nothing in order to ensure he doesn't kill ever again. Batman's desire to put an end to Napier's run is greater than his own personal well-being and outweighs what remains of his personal life. That is until Vicki Vale captures his heart.
Fear
The Joker's instability and chaos is meant to create fear within the city of Gotham in order to break down the boundaries which hold order in place. These boundaries are created by law enforcement, government officials, businessmen, et al. But when the police and governing bodies can no longer protect the people of the city, everyone immediately turns afraid of the potential for their deaths to be imminent. And this fear turns everyone against one another, even trusting The Joker over these agencies when he offers twenty million dollars to be spread out over the crowd. He preys on the weak which are found in plentiful measure once he begins to kill people.
