Captain Clown was an android used by the Joker to pilot a garbage barge he used to spread his a laughing toxin onto Gotham City.
How the Joker obtained or created the android is unknown, but it had been programmed to be loyal to the Clown Prince of Crime and an enemy to Batman. It seemed to possess an advanced artificial intelligence, as it was capable of figuring out how to cut the Batboat free from the garbage barge it was piloting before attacking Batman.
As a robot, it was very strong and almost all of Batman's attempts to stop it ended in failure. Even when Batman obtained a metal pole in which to fight it, the only real damage made was to Captain Clown's mask. However, although powerful, Captain Clown was not invincible and Batman eventually managed to crush it into a metal cube using a car masher. Joker then angrily declared, "You killed Captain Clown... YOU KILLED CAPTAIN CLOWN!".