Alias: Joker, Batman
Background: Much of the Joker's past is not known. It is known that he was incarcerated in Arkham Asylum at the time that the Aliens decided to destroy Gotham for the first time. He claims that the first Batman attempted to free him to prevent his death and claims to have thanked the Batman by killing him. Realising that without the Batman he had no function the Joker decided to take on his role and set himself up as the protector of what remained of Gotham.
With the aid of several other villains who had survived he knit the remaining citizens of Gotham into a guerilla fighting force. Like the Batman before him he did not visibly fight against the Aliens, he just ensured that most of the troops who entered the city 'disappeared' and rumours started that the city was haunted, eventually the Aliens decided to wall up Gotham and try to forget about it. When the heroes entered Gotham to try and find Batman they found the Joker instead, they asked him to join their resistance group he instead demanded that they join him. They refused and a fight broke out. The Joker fled with the heroes and died when he fell from the roof of an abandoned factory. His people were apparently loyal enough to the Joker that they attempted to hunt down the heroes, however, the disturbance draw the attention of the Aliens who levelled the city once more presumably killing the remaining population.