Bradley Cooper on Crying, Drugs, and Future 'Hangovers'

"The Hangover" actor tests his star power in "Limitless."

March 17, 2011 — -- In "The Hangover," he played the fist-pumping heartthrob, the bad boy with the big hair. But Bradley Cooper's not bent on being a summer blockbuster staple forever. He's got serious acting chops up his sleeve, which he shows off in the psychological thriller "Limitless," in theaters Friday.

That didn't make denigrating his on-screen idol any easier, though.

"I had to stand across from Robert De Niro and call him my b***h," Cooper said in a recent interview with ABC News Now's "Popcorn With Peter Travers."

Cooper stars opposite De Niro as Eddie Morra, a down-on-his-luck writer who takes a mind enhancing drug called NZT.

"What would happen if you took a drug that could open 100 percent of your brain?," Cooper mused. "I'd like to hear the person who wouldn't take it. I want to hear the argument."

NZT allows him to catapult to to top of the financial world, where he meets De Niro's Carl Van Loon, a businessman intent upon making money off of him. For Cooper, De Niro was a fortuitous foil. Years ago, as a student of Pace University's Actors Studio Drama School, he asked De Niro how he got into character for "Awakenings" only to be brushed off by the star.

How things have changed. When Cooper appeared on Monday's edition of "Inside the Actors Studio," host James Lipton played the a clip of the actor in the audience for the De Niro show. It moved Cooper to tears. Actually, he struggled to speak multiple times.

"I'm a loud crier," Cooper told audience at one point (an audience that included actress Renee Zellweger, his girlfriend since 2009). "I'm not like a sobber ... I'm like a -- it's ugly, so I apologize."

"It was way too emotional," he said on "Popcorn." "I kept apologizing to the audience."

He had an excuse: Cooper is the first graduate of the Actors Studio Drama School to be invited on the show. At first, he didn't even want to go on.

"I didn't want to do it," he said. "[Lipton] asked me to it a year ago. I thought I'd feel like a fraud up there. The blue cards would be this thick [Cooper pressed his thumb and pointer finger together], the interview would last 10 minutes and it would be over."

"Then I thought, the whole point of this show is to talk with the students. Of course I'll do it. And I'm really glad I did it after this movie."

Cooper has another, much anticipated movie on the horizon: "The Hangover Part II," which reunites him with co-stars Zach Galifianakis and Ed Helms and director Todd Phillips. The team made 2009's "Hangover" a critical and commercial success; the movie raked in more than $467 million worldwide in 2009 and won the Golden Globe for best comedy in 2010.

Cooper expects "The Hangover Part II," which takes the boys to Bangkok, Thailand, to best its predecessor.

"It felt like 'Apocalypse Now,' the comedy," he said. "The script is better than the first one, I think. Bangkok provides more material than Vegas."

Is he up for "The Hangover Part III?"

"I would do it in a heartbeat," Cooper said, "If it's a good story."

For now, he remains focused on cementing his role as a leading man. Cooper knows the success of "Limitless" will determine whether he rises to the ranks of stars like Matt Damon and Matthew McConaughey.

"There are certain moments that actually do matter," he said. "If this movie doesn't perform, it does change things. It's going to be harder to convince somebody to rest a narrative on my shoulders."