Knuckles, Vinnie and Kowalski were three thugs employed by the Joker.
Knuckles, Vinnie and Kowalski were working for the Joker during his attempt to blow up the entirety of Gotham City with an atom bomb. They held Hamilton Hill prisoner at the Mayor's very own estate while the Joker took a dip in his pool. Knuckles and Kowalski piloted the plane which was supposed to be used for their boss's getaway with Vinnie operating the rear machine gun. However, when the bomb was about to be defused by Batman and Robin, Joker ordered them to turn the plane back around. The trio, not keen on dying in the lunatics bid, tried to reason with him, but complied once Joker turned the front machine gun on them. Joker tried to force the atom bomb to explode by firing upon it, but got knocked out by a grappling device fired by an enraged Harley Quinn. This resulted in an unconscious Joker firing wildly in every direction, much to the thugs dismay, who all ducked for cover. The result was the plane crashing straight into the mayor's house. Improbably, everyone in the plane survived the crash, and the three goons emerged from the wreckage to witness Joker and Harley embracing, having reconciled their brief 'breakup'.
Joker again hired the services of Knuckles, Vinnie and Kowalski when he sought revenge on the Laff-Off competition. He introduced them as the new judges after he had successfully disposed of the old ones. Though the three easily managed to subdue Laff-Off's host, they didn't have a chance against the Dynamic Duo, who landed right on top of the three goons, knocking them out.
At some point, they were replaced as Joker's henchmen with the Three Stooges-themed Mo, Lar and Cur.