After years of stalling, The Crowded Room is finally moving forward. Leonardo DiCaprio will star in and produce the film about the first man to successfully use multiple personality disorder as a defense during a trial. Although it was recently rumored that DiCaprio was planning on taking a break from acting, the actor has had his eye on this project for almost 20 years—making it too good of a prospect to pass up.

THR reports that DiCaprio’s company Appian Way will produce The Crowded Room, based on the true story of Billy Milligan, whom DiCaprio will portray in the film. Lucky Number Slevin writer Jason Smilovic has been brought on to pen the adapted screenplay, based on the non-fiction book by Daniel Keyes. Smilovic also wrote Todd Phillips’ upcoming film Arms and the Dudes.

Keyes’ book was originally published in 1981 and tells the story of Milligan, who boasted 24 different personalities. Milligan was tried in Ohio in the late ‘70s for robbery and the rape of three women on the Ohio State University campus, but he successfully argued that his crimes were through no fault of his own; instead, Milligan blamed two of his 24 personalities for committing the crimes. Milligan was officially diagnosed with multiple personality disorder, a controversial psychiatric disorder which was renamed dissociative identity disorder, or DID, in 1994. His many personalities included “Adalana, a lesbian taking responsibility for the rapes; Ragen, a Yugoslavian communist who admitted to the robbery; and Arthur, an uptight Englishman.”

DiCaprio has reportedly been interested in playing Milligan on the big screen since 1997. A director has not yet been hired for the project, though James Cameron was previously interested in directing the film.