When it comes to The Dark Knight, Christopher Nolan's classic modern take on the Batman legend, there's really nothing that can ever upstage the dark, twisted brilliance of Heath Ledger's performance as The Joker. It was, after all, the role which - sadly posthumously - made him a legend.
There was, though, a whole lot of dark, twisted brilliance going on all over The Dark Knight set, some of which not too many people seem to know about.
And, from tiny Easter eggs involving his daughter through to his mysterious preparations for the role, there was a whole lot of odd stuff going on behind the scenes centered around the genius of Heath Ledger...
Here are seven of the most intriguing...
7. The Hospital Explosion Caused Actual Panic
The 'hospital' blown up in the movie was actually not a hospital at all, but instead an abandoned Chicago factory. All the same, the on-set explosion scared locals enough that the police received several terrified phone calls reporting a possible terrorist attack.
6. Heath Ledger Kept a Terrifying Journal
Throughout his preparation for the role of The Joker, Ledger kept a 'Joker Journal', which (over six weeks spent alone in a hotel room) he filled with the darkest, strangest and most twisted things he could think of, all in order to get into character.
Among the things he thought would make The Joker laugh? Blind babies, landmines and AIDS...
5. The Joker's Lab Coat Was Hiding a Secret
That name tag The Joker is wearing there? It reads Matilda - the name of Heath Ledger's daughter. Which is either incredibly sweet, or incredibly dark. Or, in fact, possibly both.
4. We Almost Saw a Very Different Joker
Steve Carell, Adrien Brody and Robin Williams all actively sought the part of The Joker - but Chris Nolan never wavered in his determination to get Ledger to play the role...
3. Ledger Filmed Some of His Darkest Scenes Himself
That image above, there? That's Heath Ledger directing one of The Joker's warning videos. The actor shot both of the video scenes himself...
2. Ledger Designed The Joker Himself
Directing himself wasn't the limit of Heath Ledger's active involvement in the character, though.
The incredible make-up The Joker wears throughout the movie? Ledger designed it himself, using store-bought cosmetics. The look was then replicated by the film's make-up team, using high-tech stamped silicone that would look identical for each day of filming.
1. The Joker's Most Memorable Tic Was Real
As it turns out, one of the greatest elements of Ledger's performance - the sucking at his cheeks and licking of his lips - was a side-effect of that very make-up.
Ledger originally found the prosthetic make-up incredibly uncomfortable - so he used the irritation (and his physical response to it) to add depth to The Joker as a character.