By Batman you mean the crime fighting hero of legend? Or do you mean a man with a pet bat? A man that thinks he's a bat? A man as ugly as a bat? All but the first I think we can do at this stage.
Crime fighting hero of legend. He didn't start out that way, just part way through he turned out to be a cross between Batman and Robin. His main idea came from a long ago discussion of how every shadowdancer looked pretty much the same. Rogue X / Shadowdancer. So I went as far off as possible. Plate Mail. Greatsword. Fighter X / Shadowdancer. In 3.5 I threw in some Human Paragon to get the skills I needed. With PF, I don't need to. Then I built a story around that idea. . . and it ended up being Batman's.
Circus background. Check. (Robin's technically)
Parents murdered. Check.
Takes up a life of vengeful justice. Check. (Lawful Neutral)
Hides his face. Check. (Because of scars in this case)
Likes the night. Check. (Shadowdancer)
My old LEW background, can be adjusted for the PF world.
[sblock=background]Background:A boy finds hidden strength within and pulls himself free from where he was trapped, beneath the burning wagon. The rain soothes where it falls upon burned skin as he lies in the mud. The attack is over, and the bandits have gone. All that remains is the bodies of his family. Circus folk, innocent, harmless. There had been guards, two. One lies dead, a knife in his back. The other, the traitor, has fled with his share of the spoils.
The boy lifts the fallen guard's sword. He barely has the strength to carry it, but he moves surely into the forest, after the traitor. The night is dark, the trees crowd near, stifling him. In a clearing sits the traitor, counting his money. The darkness conceals until it is too late. A sword rises, and then falls. Alone in the clearing, a boy falls to the ground and weeps.
The next morning a young man walks into the world, his sword at his back. He is still weak, and has much to learn. But he has a strong will, and a desire for justice.
Five years later, a man walks down the road where he lost his family. No evidence remains, but his heart remembers. He is stronger now, and has honed his skills. Perhaps the time has come. Perhaps he will never achieve revenge for himself, but he will work to ensure that injustice happens to no others. He has heard tales of the inn of the Red Dragon, that is where he will start his quest. He turns away from what his heart remembers and takes a new step.[/sblock]