According to the director, Denis Villeneuve, Javier Bardem was offered the lead role but the actor felt he didn't suit the character. Christian Bale was also offered the role and he wanted to do it but couldn't due to scheduling conflicts with other projects.
One of two movies released in 2013 about characters meeting duplicates of themselves. The other was The Double, staring Jesse Eisenberg. The films are also both based on novels called The Double, but the books and films are otherwise unrelated.