Quackerjack is an anthropomorphic duck.
Quackerjack used to be the owner of a toy company, Quackerjack Toys, until the competition- especially video games- killed his products. This turn of events drove the toy maker mad and onto the criminal path, through which he could continue his company outside of rules and regulations. He gained three goals as a result: monetary gain, to revive his brand, and to crush the competition and erase videogames from existence. Armed with a wide array of dangerous toys and his "sidekick", inanimate stuffed toy "Mr Banana Brain", Quackerjack proceeded to terrorize St. Canard.
Quackerjack's criminal actions brought him to the attention of Darkwing Duck, and the two became foes. Quackerjack eventually joined the Fearsome Five, a group of supervillains dedicated to taking down Darkwing.
Shortly before the Quackwerks Corporation's takeover of St. Canard, Negaduck revealed to Quackerjack that he had discovered Darkwing's secret identity. Quackerjack begged to be let in on the secret, but Negaduck refused, telling Quackerjack that he was just not mean enough, before ripping Mr Banana Brain to shreds. This caused Quackerjack to snap, declaring that he would prove that he was, in fact, mean enough. However, Quackerjack was, soon after, forced to take a job at Quackwerk's toy department, putting his evil plans on hold. Happy to be working at a toy company again, Quackerjack briefly attempted to turn over a new leaf, even finding a girlfriend, Claire. This was not to last, though, as Quackerjack soon realized that the toy department executives would not listen to any of his (extremely dangerous) toy ideas.
Deciding to take his revenge after all, Quackerjack kidnapped the other members of the Fearsome Five (besides Negaduck), convincing them to reform the team as the Fearsome Four with him as the leader. The Four went up against Darkwing again, but were defeated as always. After a series of evil crimes, including taking over the video game company which put his toy company out of business and turning its employees into toys, Quackerjack finally tired of being "mean enough", turning himself into a toy on Claire's doorstep, along with a note telling her that he believes this is the best he'll ever be. Whether or not Quackerjack is still a toy is debatable.