Ethan Hawke and John Goodman have reportedly boarded "Valerian and the City of a Thousand Planets," director Luc Besson’s adaptation of the classic French sci-fi comic.

The filmmaker announced Hawke's involvement over the weekend on Instagram, while TheWrap reported this afternoon that Goodman is nearing a deal to lend his voice to a CG alien. The two join a cast that includes Dane DeHaan, Cara Delevingne, Clive Owen and Rihanna.

Created in 1967 by Pierre Christin and Jean-Claude Mézières, the influential comic series follows time-traveling hero Valerian and his sidekick Laureline, who serve as guards against temporal paradoxes and then become freelance troubleshooters when their home disappears from space-time. “Valerian” has sold more than 10 million copies in 21 languages.

DeHaan (“Chronicle,” “The Amazing Spider-Man 2″) will play Valerian, while Delevingne (“Paper Towns”) has been cast as Laureline. Besson (“The Fifth Element,” “Lucy”) will write and direct, with Virginie Besson Silla producing on behalf of EuropaCorp.

"Valerian and the City of a Thousand Planets" is scheduled to arrive in theaters on July 21, 2017.