It's no secret Jared Leto knows how to act and can get really into the parts he plays. Many can't wait to see the Academy Award winner's latest role in "Suicide Squad" as the Joker, especially after images of him with the slicked back green hair, silver teeth and tatoos were shown in the first trailer. Leto threw himself deep into the role, so much so that his co-stars feel they don't even know him. 

During an interview with Beats Radio 1, Will Smith said he has "never actually met" Leto. The only time on set they exchanged words was when Smith was playing Deadshot and Leto was the Joker. Smith said Leto was "all-in" on the part.

"We worked together for six months and we’ve never exchanged a word outside of ‘Action!’ and ‘Cut!’ I literally have not met him yet. So, the first time I see him will be 'Hey, Jared. What’s up?'" Smith dished.

Smith isn't the first co-star to speak about how locked into the role Leto was. Margot Robbie, who stars in "Suicide Squad" as Harley Quinn, told the New York Daily News in August that Leto was intimidating at first, but now she said she's more afraid of him without the Joker makeup than with it.

"I saw him out of makeup once and I was actually petrified of him. I was too scared to go up and didn't know who that person was, and when he got back into his makeup I was far more comfortable," she said.

In June, Adam Beach, who plays Slipknot in the upcoming film, told E! News that as part of his method acting Leto sent gifts to a few of his co-stars. He reportedly sent Robbie a letter with a dead rat and Smith a letter with bullets.

"He encompasses this beautiful man and he shows it in, 'Hello, how are you?,' but in an instant, he goes to psychotic behavior where you're in fear," Beach dished about Leto's performance. "But you love him because he has both of those genuine sides."

The role of the Joker can be a very mentally demanding role as many have experienced. "Suicide Squad" director hired an on-set therapist for his cast because he didn't want them to take their work home with them, especially based on what has happened with past portrayals of the Batman villain.

Leto wasn't the first actor to go all-in on the part of one the most psychotic comic book villains ever. Sometimes the part can really consume you, like what unfortunately happened to the late Heath Ledger.

When Ledger took the role as the Joker in 2008's "The Dark Knight" he completely immersed himself in the character, which many believe led to his death prior to the film's release. In August, Ledger's personal diary surfaced in a German documentary. According to Entertainment Weekly, the diary was filled with pictures from the Batman comics, playing cards, and the word chaos was written in all caps.

Jack Nicholson, who played the Joker in Tim Burton's 1989 "Batman" told the New York Daily News in January 2008 that he warned Ledger about the toll the role can play on a person. Ledger reportedly was getting very little sleep and the part had wore him down mentally and physically. Ledger died on Jan. 22, 2008 at the age of 28 after an accidental overdose in his New York City apartment.

"Suicide Squad" hits theaters Aug. 5, 2016.