The Joker, The Clown Prince of Crime, Harlequin of Hate. No matter what you call him The Joker has always been a force to be reckoned with since he was first released in 1940. The first drawing of him was created by Jerry Robinson and has gone through many incarnations since. From being a grinning killer in Batman #1 to a mischevious prankster in the 50s and 60s and then back to his psychotic and crazy nature in the 70s and has lasted ever since.
Dropped into a vat of chemicals and flushed out into a river after a botched robbery by Batman. The former Red Hood emerged with chalk white skin, red lips, and green hair and started calling himself The Joker. Blaming Batman for his resulting condition he set forth on a career to irritate The Dark Knight whenever possible. However, he didn't just stop at cynical jokes and pranks. Throughout time The Joker has killed or severely injured major players not only in the Batman books but throughout DC. Shooting the first Robin, Dick Grayson, which initially causes Batman to "fire" him because it's too dangerous. Crippling Barbara Gordon and kidnapping Comissioner James Gordon in an attempt to drive him insane to prove that just one really bad day could make any man insane, during the book Batman: The Killing Joke. Then, beating the second Robin, Jason Todd, to near death and then blowing up the building he was in, during the story A Death In The Family. Also, shooting Comissioner Gordon's wife Sarah Essen in the head during the conclusion of No Man's Land. Not to mention almost killing The Huntress while she was trying to protect a building full of civilians. He has also contended with several other heroes including The Creeper, The Flash, and even Superman. That doesn't account for the thousands that have died by his joker toxin.
Despite the 1989 Batman movie, The Joker doesn't have a real name. He has always been known as The Joker. DC comics has never actually given him a definitive name in publication. Also, he's never really had a definitive origin either, except for one major part, which is him being dropped into a vat of chemicals. It's not the Joker if his skin isn't permanently white and hair is green. Although there are different interpretations when it comes to his lips, sometimes they are naturally red (which is what I prefer) and sometimes he does paint them.
Several people have portrayed the Clown Prince of Crime over the years in animation, tv, and movies. Including Mark Hamill, who in my personal opinion is the best and definitive Joker, even if it is just his voice. Other actors that have taken on the smile over the years include Ceasar Romero, Frank Welker (also known for Scooby Doo), John Dimaggio (also known for Bender from Futurama), Kevin Michael Richardson, Jack Nicholson, and Heath Ledger (who in my opinion isn't the Joker at all, but that's for another article.)
His unpredictable nature makes him feared not only by heroes and civilians but with other villains as well. Even Lex Luthor is wary of him.
Even though there have been several versions of the Joker one thing is true. He is the most recognized villain, not only of Batman's but of the DC Universe itself. And as the man says, "If I'm going to have a past, I prefer it to be multiple choice."