According to Vin Diesel, Universal Pictures agreed to green-light Riddick knowing it would be rated R, now we know that that is true. Written and directed by David Twohy, the film has earned its R rating for "strong violence, language and some sexual content/nudity." There was some worry that the film might be rated PG-13 -- while Pitch Black had an R rating, its sequel The Chronicles of Riddick was PG-13.
The infamous Riddick has been left for dead on a sun-scorched planet that appears to be lifeless. Soon, however, he finds himself fighting for survival against alien predators more lethal than any human he's encountered. The only way off is for Riddick to activate an emergency beacon and alert mercenaries who rapidly descend to the planet in search of their bounty.
The first ship to arrive carries a new breed of merc, more lethal and violent, while the second is captained by a man whose pursuit of Riddick is more personal. With time running out and a storm on the horizon that no one could survive, his hunters won't leave the planet without Riddick's head as their trophy.