Since apparently Leornardo DiCaprio has shown no interest in the role of the Joker in the upcoming live action Joker origin film directed by Todd Phillips, the director has shifted his eyes in the direction of Joaquin Phoenix, star of such movies like Signs, Gladiator and the older one, The Master. Not sure what makes Phillips so interested in Phoenix now, but it seems to be his portrayal of a man slowly falling into madness in The Master what has brought him closer to snatching the role.
Unfortunately, I would not count him in yet, since he had been considered for other superhero roles like Lex Luthor in Batman v Superman: Dawn of Justice, (which I would have wanted him to have instead of the final choice), and Doctor Strange and passed on both occassions. Guess we will have to see what happens with Joaquin and probable other candidates that will surely arise before filming starts.
Here are some links to of some of the most important news coverage on the subject for those interested: