Galactus and The Dark Phoenix eat planets and suns. The Red Skull cashed paychecks directly from Hitler himself. But ask your average person who the scariest villain in comics is and they'll choose either Lex Luthor, Magneto, or The Joker. Lex is a MENSA level billionairre who hates aliens and poor people. Magneto is a Holocaust survivor with the power of magnetism (he's not so much a fan of Red Skull). But The Joker is perhaps the most terrifying of all. He has no super powers, no millions of dollars, he's merely a sociopath with a sense of humor, and a very complicated relationship with Batman.
But where does The Joker come from? What set him on his life of crime? Who was he before he showed up in Batman's rogue gallery? What's his real name?
What makes The Joker an effective villain is that those questions have never really been answered. There's no Holocaust in his background. There's no absuive parents. No orphanned when your parents threw you out of an airplane before they were enslaved by aliens. The Joker occasionally offers a piece of his past, but will later contradict it. A gag that's used beautifully in The Dark Knight.
So, given The Joker's muddled history, it's not much of a surprise that, even by comic book standards, his continuity is an erratic mess. Several writers have written origins or first appearances for The Clown Prince Of Crime. Most notably in recent years, Ed Brubaker and Michael Green.
Lovers and Madmen by Michael Green serves as a possible origin story. An expert thief gets bored of how perfectly he executes his crimes and contemplates getting out of the business when he runs across Batman, and becomes obsessed. (There's a fun little scene in a bar where "Jack" discusses his boredom at work with a blonde psychology student who calls him Mr. J.)
During "Jack"'s crime spree, Bruce Wayne meets a woman named Lorna. The introduction of a love interest in a story involving The Joker can only mean one thing. She gonna die. And, of course, Batman has to watch. With Lorna bleeding in his arms, he decides he can't go after Jack, so he tosses his baterang after him, marking his face into a permanent smile.
Now willing to do whatever it takes to pursue Jack, he calls in a favor from the mob, and consults a Gotham psychiatrist named Jonathan Crane, who labels Jack's methods insane. While the mob is holding him, Jack escapes and gets in a gun/fist/lead pipe fight with his captors, and ends up falling into a vat of anti-psychotics. Voila, Joker. Whose first two acts are a crime spree, and an act of altruism (paying all of the future Miss Harley Quinn's college expenses).
Also, it turns out that Lorna doesn't die, but decides Gotham isn't safe, and Julie Madisons out of town.
Story: 4/5, Art 3/5
The Man Who Laughs doesn't bother with The Joker's past, but focuses on his first crime spree in Gotham. It could almost be a follow-up to Lovers And Madmen, except that Gordon and Batman are unfamiliar with The Joker, despite having arrested him at the close of Lovers And Madmen. The whole story is pretty much a three issue summation of a Joker story. There's gas, there's the relationship between Batman and Gordon, and Batman blaming himself from creating The Joker. This story also outs Gordon as being associated with Batman, allowing him to create The Bat Signal.
Story 3/5. Art 4/5
The Man Who Laughs trade paperback also features a backup story,with pencils by Patrick Zircher, called "Made Of Wood". If you're reading this for chronological sake, put the book down as this story comes waaaaaaay later in The Batman mythos.