Short answer: he doesn't have one. Long answer:
It's changed throughout the years, but for the post Denny O'Neil era, he didn't have one. A major part of Alan Moore's The Killing Joke is Joker flashing back to memories of himself as a struggling comedian who had "one bad day," but Joker himself discounts the flashbacks at the end with the statement "sometimes i remember it one way, sometimes it's another. If I'm going to have a past, i prefer it be multiple choice." Whilst there have been events in recent years to establish the past given in TKJ as cannon, the general understanding is that Joker himself doesn't know who he was before anymore. The Dark Knight references Joker's shifting memories with the various stories about his scars.
Lucia
Believe
bosch
yes.
What is the product of th e prime factor 344
Kirsten Ramirez That is a sexy cute funny all in one!(kirsten ramirez is my name!)
Referring to playing cards, it means 2 Jokers in Every Deck
Hail to the Chief.
linseed
what the enemies fo th e strawberry frog what the enemies fo th e strawberry frog
tiger
th e owner