While we never learn his real name, Quackerjack was a toymaker, run out of buisness by the popular videogame series, Whiffle Boy (basically Mario) He went insane, and started to use weaponized toys to destroy the video game's, and all their tie ins. Once he was stopped by Darkwing several times, he would start trying to get his toys, not believing the fact that they were dangerous was why they weren't being bought by parents. At one point in the show, his doll, Mr.BananaBrain, was possessed by the evil spirit, Paddywhack. The spirit fed on the misfortune of others, and trapped quackerjack inside it's haunted jack in the box. Once Darkwing was sucked inside as well, he was forced to team up with Quackerjack, pulling pranks on each other until Paddywhack was deprived of the sorrow he fed on. for the rest of the show's run, he mostly teamed up with his best friend, Megavolt. However in the graphic novels, things began to change. When Saint Canard was taken over by the evil corporation, Quackerwerks (not owned by Quackerjack) he went back to being a toymaker. However he was driven more and more enraged when his bosses kept denying, changing, or stealing his ideas. He eventually snapped a second time, and became a much darker, more violent version of himself. Once he helped Darkwing stop Quackerwerks, it is revealed he now had a deep hatred for Negaduck. It turns out that Negaduck had known Darkwing's secret identity, but refused to him, do to Quackerjack not being "Mean Enough". Negaduck tore apart his Mr.BananaBrain doll, making his insane state even worse. The last time Quackerjack appeared, he was using a ray to turn people into plush toys. It was revealed during this time that Quackerjack had a girlfriend named Claire, who he left behind after he left his job at Quackerwerks. After being defeated yet again, Quackerjack turned himself into a plush toy at his girlfriend's doorstep, saying "It's the best i'll ever be" Quackerjack is a mix of the Joker, and the Toyman. Both from DC comics. However during the episode with Paddywhack, he was shown to have been confused at how his doll was speaking in a new voice, but didn't seem surprised it could move around on it's own, and was alive. This suggests he was also inspired by the lesser known Batman villain, the Ventriloquist.
Mr.BananaBrain
Paddywhack
Quackerjack attacking a video game convention with his toy beam