Stellan Skarsgård says Robin Williams couldn't stop himself from doing pranks and 'crazy takes' while making 'Good Will Hunting': 'He had to get it out of his system'

• Stellan Skarsgård recalled working with Robin Williams in "Good Will Hunting."
• On set, Williams was constantly pulling pranks — and Skarsgård loved it.

One of the main memories Stellan Skarsgård has from filming his scene-stealing performance in the 1997 hit "Good Will Hunting" was how much energy Robin Williams had on set.

Though the project, penned by Ben Affleck and Matt Damon, was a dramatic look at a misguided math genius (Damon) who builds a bond with a psychologist (Williams), the set was often filled with pranks and antics courtesy of Williams.

"He was extremely funny. And we laughed," Skarsgård told Business Insider in our latest "Role Play" interview. "It was a shoot where it was OK to laugh and do a couple of crazy takes."

Skarsgård, who plays the professor trying to help Damon's character harness his potential, said there were times Williams would do a whole take in the voice of Robert De Niro or Jack Nicholson. Other times, he would beg director Gus Van Sant for one more take because he had a funny idea.

"The thing with him is he had to get it out of his system," Skarsgård said. "He would have an idea about something funny, and he would have to get it out for him to continue. We would do 10 takes on something, and it was good, and Gus Van Sant was pleased, and Robin would say, 'Can I do one more take?' And then he had to get it out of him. He was fantastic to work with."