Despite the fact that the Joker is their original owner, Harley Quinn is the one who really cares about them. Indeed, Bud and Lou like her better than the Joker, if it comes to that; because Harley feeds them, keeps them company, and often sits around and lets them lick her.
It is proven that the Joker doesn't care about Bud and Lou when he rigs a bomb to destroy Gotham, but forgets to bring them on the plain. He decides to leave them, and tries to force Harley onto the plane. But Harley kicks him and jumps out of the plane.
Bud and Lou often get cranky when Harley isn't around, as is demonstrated when the Joker gets angry at Harley and (quite literally) kicks her out. The Joker regrets this, because not only does his lair fall into chaos without Harley around to keep it organized, but Bud and Lou become hostile toward him.
Despite the fact Bud and Lou seem harmless and incompetent, they actually aren't. They will attack (and sometimes kill) Harley on the Joker's command. They have also proven to be intelligent; for no matter how many times their masters are separated from them, Bud and Lou find them eventually.
Bud and Lou serve as recurring villains in the Cartoon Network series Krypto the Superdog. In the series, they battle against Batman's dog Ace and Superman's dog Krypto.
- They are a reference to the famous comic duo Bud Abbott and Lou Costello, creators of the famous "Who's On First?" Skit.
- In Batman: Arkham City the Penguin shot them and put them on display in his museum.