Yet Cooper had never anticipated playing the lead in a story he had been discussing with his friend for more than a decade.
"I was really nervous about this role because first of all I felt a tremendous responsibility and I felt especially stressed as we had never talked about the idea of me playing Rory, ever," Cooper recalls. "I really didn't know I could do it. But I remember when I was in Paris on vacation with my mum just a week before we started shooting and I read the whole thing again in a cafe and somehow it just clicked."
Written and directed by Klugman and Lee Sternthal, The Words follows the struggle of novelist Rory Jansen who, having delivered a best-seller must face the truth - he didn't write it.
He finds an old manuscript hidden inside an antique briefcase his wife give him on a trip to Paris. He decides to pass it off as his own. Only having made his name, its real author (Jeremy Irons) tracks him down.
"Rory's a guy who so desperately wants to be special and he's a little impatient," says Cooper. "The film asks if he can live a life of benefiting from that success without ever having done the work. What makes this different from other movies that might be in a similar vein is that Rory really does it without any malice or pre-meditation.
"He sort of falls into it and creates this wonderful moral tapestry. Does he have to take responsibility for what he did?"
The film's cast includes Zoe Saldana as Rory's wife, Dennis Quaid and Olivia Wilde as well as the veteran Irons.
"I play this guy whose life has sort of peaked when he wrote this screenplay and lost it and who had lived on through that, having had his writing spirit sort of de-balled, and he never wrote anything again," says Irons.
"Everyone was telling me about Bradley. You know these young guys who sort of are taking over the business ... as an old man you have to try to keep up to date and if you can't be them you have to be in the same shot as them," he laughs.
Cooper, who became friends with Robert De Niro while making Limitless - another film about artificially contrived talent - was particularly keen to work with Irons.
"Oh man, what was so crazy is that The Mission is one of my favourite movies and Jeremy and Bob worked together on that.
"So whenever I got comfortable enough I would just start asking Jeremy a barrage of questions about the movies he had done."
The Words has had mixed reviews in the US where its box office has been trickling toward doubling its small budget since its release a month ago.
Cooper, who had insisted on considerable re-writes before signing on for The Hangover, is now ready to direct.
An avid reader, he has a lot of books he would like to turn into movies.
And Klugman will be there right alongside him.
"Honestly, the truth is I don't do anything without him" Cooper says only half-joking.
"If I direct a movie I want him to produce it with me.
"But we do this anyway. I respect him so much. I show him everything."
Who: Bradley Cooper
What: The Words, also starring Jeremy Irons and Zoe Saldana
When: Opens at cinemas Thursday
-TimeOut
