Corrupt businessman Curtis Base has decided to turn to a full life of crime and replace who he believed to be one of the best and most recognizable villains—The Joker. To that end, he succeeded in shooting the original Joker and leaving him for dead and began a crime wave with a series of gag-based murders.
Unfortunately for Base, he did not completely succeed in killing the original Joker. Base and the original Joker ended up battling for the exclusive right to be called the Joker. The fight ended between the two in a draw as Batman basically ended the struggle and took the original into custody. Base rarely resurfaced as the second Joker after his second run in with the original.
Currently it is presumed that Base is dead or changed his mind to succeed the Joker.