(This article is coming to life purely out of a need to set right the hundreds of speculative ones.)
He is an actor recognized for not only taking on a role, but becoming it. Jared Leto is one of our generations greatest method actors; known for movies such as Requiem for a Dream, Fight Club, Lord of War, and Dallas Buyers Club.
There have been many times Leto has risked his health and life for a role. Refusing to commit to acting alone, he will immerse himself in the life of his character, often living like them for extended periods of time. Sometimes this means morbid obesity or emaciating starvation, and all the health issues that come with it. He has spent months dressed as a female to portray a trans woman in Dallas Buyers club; similar time on the streets preparing to become a heroin addict for Requiem for a Dream; and even learned Russian for Lord of War.
So it only made sense that he would literally "become" The Joker; instilling a very real fear in many of his fans and followers. This was a realistic concern that was only exacerbated by the death of fellow method actor Heath Ledger, attributed to losing himself inside the head of the very same DC Super-Villain. The difference between the two men is that Heath Ledger would leave The Joker on set; Jared Leto has outright refused to leave some characters at work.
When rumors of Leto playing the role of The Joker in Suicide Squad started circulating, everyone had the same questions in their heads: Would he stay in character for the entirety of filming? Should we be worried about him? The answer is a simple No. Jared Leto has obviously made some very careful decisions in regards to this role, working hard to stay grounded, while giving The Joker the respect he deserves.
First, lets discuss his lifestyle. As a health junky and fairly strict Vegan, he will only smoke, drink, or eat animal products if no other options are available (such as realistic substitutes). He avoids salts and processed sugars, and whenever possible, will choose holistic approaches to healing over pharmaceuticals. With the exception of needing the assistance of milk products and sugars to gain weight for Chapter 27, he has been committed to this healthy lifestyle for over 20 years. While Leto has admitted having to shift his eating to assist in muscle gain, he is still dedicated to a healthy diet. (Sources: 1, 2)
Second, his workout regime. While being someone who loves to spend time in nature hiking, he is also conscious of avoiding standard forms of transportation as much as possible; preferring his bicycle to cars. Leto is also a long time practitioner of Yoga, setting aside time daily for it. Yoga is a strenuous form of fitness capable of pushing your body to its limits; it also reduces stress, while improving flexibility and strength. The mental health benefits for practicing Yoga almost surpass the physical: helping to naturally alleviate chronic conditions, such as depression, pain, anxiety and insomnia. These are all issues that we know plagued the actor who last played The Joker, and directly contributed to his unfortunate passing. (Sources: 1, 2, 3, 4)
Third, his creative pursuits. Many people know that Jared Leto is the front-man for the band 30 Seconds to Mars, but may not know how involved he is. Not only has he continued doing small music gigs during filming breaks, he still has tour stops scheduled in the last leg of his current CD's release. He also writes music almost incessantly, plays guitar and piano; I guarantee he has an instrument in his trailer to keep him occupied between takes. Leto is also a multi-medium graphic artist, known for assuaging stress or boredom by sketching or drawing on any available surface. Aside from exercise, art and music are the easiest ways to release endorphins, dopamine, and serotonin into your brain. (Sources: 1, 2)
Fourth, the people that matter. Instead of shutting others out and becoming reclusive, he is doing the opposite and throwing himself into the lives of his family, friends, and fans. Keeping his mother Constance nearby, he has been travelling between Toronto and New York on his days off. Leto has been spotted with people from his social circles; going to museums and art exhibitions. Next, his addiction to social media may be relevant, but the real connection is through VyRT.com, a digital and social platform he developed. On VyRT, he has been staying in touch, and being involved directly in discussion with his fans and followers. At least once a day he joins his designated chatroom to talk about whatever the topic is at the moment, or to offer up inspirational pieces of advice. While he has become an expert at evading any Suicide Squad or Joker related questions, much to the frustration of eager fans, he happily shares about the rest of his life and what he is doing in his spare time. (Sources 1, 2, 3)
I am aware that in sharing all of this, some of you may be concerned that he isn't as focused on his role as he should be. I would beg to differ. Heath Ledger's Joker was one of a kind, and very specific to the style Christopher Nolan needed for The Dark Knight. To get into character for a series of movies that dark would require total immersion. Some would say that it was Ledger's deep internal suffering, which developed due to the immersion, that made the Joker who he was.
Based on the bits and pieces we have put together from leaks, hints, and cues from the comic book series; Jared Leto is right where he needs to be to play the current incarnation of The Joker. Described as being "Shakespearean" in nature, the character would be a combination of comedy and tragedy, colour and flamboyant exaggeration. For an individual who has dedicated his life to art in its many forms, Leto is totally in his element with this character. I can see this as being the role he has been waiting for; a challenge for every aspect of his creativity.
So for someone who doesn't know who Jared Leto is, outside of the movies he has done, you may have had your concerns. Let me help put those concerns aside, while also silencing some of the speculation. This version of The Joker is a colorful, sarcastic, sadistic and happily insane character; he will make you simultaneously laugh while being uncomfortable. There is no one better cast to fit that list of attributes, and no one better to maintain the exact lifestyle needed to fit the part.
(Check out this link from batman-news.com to watch all the current videos of Jared Leto in action as The Joker)