Given a reference text about Justice League Dark, tell me who the main actors are and what roles they played.

Context: Justice League Dark is a 2017 American adult animated science fantasy superhero film produced by Warner Bros. Animation and distributed by Warner Home Video. Featuring the DC Comics team of the same name created by Peter Milligan and Mikel Janín, the film is the 27th of the DC Universe Animated Original Movies and the eighth of the DC Animated Movie Universe. Unlike most installments in the DC Animated Universe Movies series, Justice League Dark features an original premise. The film stars Matt Ryan as John Constantine and Jason O'Mara as Batman, reprising their respective roles from previous media. It was released on Digital HD on January 24, 2017, and on DVD and Blu-ray on February 7.

A sequel, Justice League Dark: Apokolips War, was released in May 2020.

Answer: The main actors in Justice League Dark were Matt Ryan and Jason O'Mara. In the film, Matt Ryan is John Constantine and Jason O'Mara is Batman.