Mark Hamill (Star Wars) is the voice of the Joker to the ears of a generation...or two. In the early 90's, he took a hold of the Joker in Batman: The Animated Series and never looked back. He has voiced the maniacal clown on TV, feature films, and in video games for three decades. Hamill has been more picky about his projects as the Joker for several years now. However, on numerous occasions he has mentioned that he would love to come back, if WB would ever dare make an animated version of The Killing Joke.
The storyline was written by Alan Moore and is one of the definitive Joker tales in the comics. Where the Joker puts Batman, Commissioner Gordon, and Barbara Gordon, through a night of psychological terror and all forms of emotional, sexual, and physical assaults, that would be fit for the movie, Se7en. For years the dark material was thought to be unfit for WB/DC's animation tone, however the studio has been gradually increasing the maturity level of their animated films. Most recently, Batman: Assault on Arkham and Justice League: Gods and Monsters, showed that the envelope can be pushed and people will respond. So the time is right for the Joker's greatest joke to be told.
There has been a long-standing debate over exactly how the ambiguous ending of the The Killing Joke really played out. It will be interesting to see how it will be adapted for film and how people will respond to the movie, who may not have read the comics. It's truly a dark tale and it's logical to wonder if they are positioning parts of the story to be interwoven into the live-action universe. Much like Assault on Arkham was the primer for the live-action movie version of the Suicide Squad. There is no presence of either Commissioner Gordon or Barbara/Batgirl in the Batman vs Superman trailer, so it is possible that part of Batman's rage is about the loss of all of his Bat-family at different points in his career.
According to the report by Collider, Hamill has already completed his voiceover work for Batman: The Killing Joke. Legendary creator Bruce Timm is producing as well, so even though details are scarce at this point on the cast and crew, rest assured that the iconic story is in capable hands. Hamill is riding a wave of success in his live-action career, with appearances in Kingsman: The Secret Service, The Flash, and [Star Wars: Episode VII — The Force Awakens](tag:711158), that he hasn't enjoyed in years. Hopefully his new found swagger, combined with his unabashed love of the The Killing Joke, will result in a Joker performance for the ages.
Batman: The Killing Joke will be released straight to video in 2016.
Source: Point of Geeks