The 66-year-old Dark Knight producer opened up about the 43-year-old actor in an interview with Collider published Thursday. Leto plays the Joker in the forthcoming movie, and lived as the DC Comics character while filming.
"It was different, it was fun," Roven said of the star's technique. "The group first wasn't sure because the [assistant directors] had to call him 'Mr. J' to get him to come to the set. And he did in many ways isolate himself from the rest of the group, but that's really what his character was."
"[It was] the purpose of his character in many ways, other than when he was with Harley [Quinn] or trying to get Harley," he added. "It was very entertaining, it was fuel for a lot of good sport and a lot of laughs and his isolation bonded the squad."
Will Smith, who portrays Deadshot in the movie, recently told Beats 1 Leto went "all in" on the Joker, to the point of him having "never actually met [the real] Jared Leto." The actor sent his co-stars gross gifts as the Joker, including a live rat and a dead hog.
Margot Robbie plays Harley Quinn, with Joel Kinnaman as Rick Flag, Cara Delevingne as Enchantress, Jai Courtney as Boomerang and Viola Davis as Amanda Waller. The film is directed by Fury helmer David Ayer, and opens in theaters Aug. 5, 2016.