If you’re going to call your sci-fi movie “Valerian and the City of a Thousand Planets,” you’d better be sure Valerian (Dane DeHaan) is a guy your audience can get behind.

Director Luc Besson styles him as a cocky space rogue, but Valerian is weak sauce. And so is this movie.

Based on the French comic “Valerian and Laureline,” Besson’s film omits the duo’s other half from the title. Pourquoi?

Cara Delevingne, as Valerian’s partner in intergalactic intelligence missions, is the stronger player here. She spends too much time flicking away random marriage proposals from Valerian, though they have zero chemistry.

DeHaan, who’s been good in other, quieter films, is not the guy for this part. No wonder his lame come-ons sound wooden.

When not bickering, the pair adventures through one extravagant 3-D, CGI alienscape after another while trailing a band of alleged terrorists, who are a race of lithe, iridescent utopia-dwellers called Pearls. Their prologue, paired with a chronology of intergalactic diplomacy, is the film’s one solid bit.

The Pearls are trying to recover a key to their planet’s restoration. The key, too, seems to be called a pearl. They have a pet who eats the pearl and poops out more pearls. It’s all Saturday morning cartoon-level stuff, and if the target audience of this mess was 8-year-olds, I’d totally get it.

But then along comes Ethan Hawke as a space pimp, and Clive Owen as a torture-happy officer, and Rihanna as a shape-shifting exotic dancer, so I guess it’s not really for the kiddies. I’m not sure whom it is for. Maybe RiRi’s fans: She’s far more engaging than either our heroes or Besson’s splashy digital theatrics.