Heath Ledger was dynamite as the Joker in “The Dark Knight”, so much so that everyone on set was terrified of him. Legendary actor Sir Michael Caine even stumbled over his lines during scenes with Ledger. It would be a regular occasion to find the actor acting like a recluse, drawing disturbing doodles in his dressing or hotel room.
It didn’t just stop there. The actor was abusing prescription pills, suffering from insomnia, and depression. The film is regarded as the thing that ultimately sent him over the edge.
Christian Bale – The Machinist
The actor is known for pushing the limits and immersing himself deep into certain roles, both physically and mentally. In the film "The Machinist", Bale played the hallucinating machinists with insomnia. He lost 60 pounds for the role, making himself completely emaciated. The actor didn't get much sleep either and would go for weeks fully awake.
The actor would also go as far as completely isolating himself from the outside world for months. All of this of course made his acting on the film absolute perfection.
Bill Skarsgard – It
Playing a demonic clown is bound to create some problems with your mental state. Bill Skarsgard can certainly attest to this. The horrifying clown got a real upgrade when the actor took the reigns on this one. There is no denying the sheer terror when watching this film, which is surprising, considering the fact that he didn't have much experience beforehand.
Thanks to the film, the actor instantly shot to stardom. He now will forever be remembered as the greatest Pennywise ever. That fact remained true in the sequel.
Daniel Day-Lewis – My Left Foot
Regarded as one of the greatest actors of our time, Daniel Day-Lewis went off the rails in the film "My Left Foot." In the film, he played a disabled hunchback. During the duration of filming, the actor remained in that position, leaving him with two broken ribs by the end of the production.
The Lincoln actor was practically in a state of self-imposed handicap, refusing to come out of character. The crew even had to spoon-feed him.
Jared Leto – Suicide Squad
After watching Jack Nicholson and Heath Ledger portray one of pop culture's most iconic characters, Jarred Leto was determined to do as good of a job as possible! His preparations were intense and involved him sending weird gifts to his co-stars. The Joker, ahem, Leto, sent Margot Robbie disturbing love letters and a dead rat. Will Smith who played Deadshot was lucky enough to receive bullets in the mail. Nice.
Apparently, therapists had to show up on set to help the actor get through the role as his sanity was beginning to be questioned. Unfortunately for him, Jaoquin Phoenix blew that all out of the park a couple of years later with his version of the Joker.