Bud and Lou are Harley Quinn's pet hyenas. They're extremely loyal to her and she refers to them as her "babies".
One time, they were stolen by some white collar criminals who tried to sell them in an auction as exotic animals. However, Harley found the place and destroyed the whole racket with help from Poison Ivy and recovered her pets.
After they ate several pet dogs surrounding their hideout, Catwoman donated the two hyenas to the Gotham Zoo.
When Joker returned to Gotham after a year hiatus, now wearing his disembodied face skin as a mask, he attempted to get Harley to conform to his new brand of craziness with him by cutting off her face as well. In order to drive her to that point of madness, Joker infected her former hyenas with rabies and commanded them to attack her. Unable to fend them off, Harley was forced to break their necks, killing her beloved pets. 
- 12 Appearances of Bud and Lou the Hyenas (New Earth)
- 3 Images featuring Bud and Lou the Hyenas (New Earth)
- Quotations by or about Bud and Lou the Hyenas (New Earth)
- Character Gallery: Bud and Lou the Hyenas (New Earth)