Comedy star Billy Crystal returns to one of his favourite roles of all time — the roly-poly cyclops Mike Wazowski — with this summer's star-studded animated kids' comedy Monsters University.

"I love this guy. Mike is, I think, the favourite character I've ever played in anything I have ever done. I love him because I love his attitude. I love his inner strength. I love his sense of humour. I love that he never stops believing in himself and in other people and I think it's kind of great," the veteran funnyman told CBC's Jelena Adzic.

Monsters University comes 12 years after Pixar's 2001 hit Monsters, Inc., but goes back in time to explore how Crystal's diminutive character first met his work partner, the burly Sulley (voiced by John Goodman). As with the original, the prequel story features a cast of popular actors, including Steve Buscemi, Helen Mirren, Frank Oz, Sean Hayes and Dave Foley.

Canadian actor Foley, who has previous Pixar animation experience as the star of 1998's A Bug's Life, shares much of his Monsters University screen time with Hayes: they portray the two-headed, conjoined monster Terry and Terri. Though he didn't meet his co-stars of A Bug's Life until much later, this time around Foley was lucky to record his part alongside Hayes, which meant he could improvise.

"We were able to talk over each other and snipe at each other as brothers would," Foley said, adding that voice roles are much harder than people would think, with actors typically forced to concentrate on performing scenes with little more than a description as reference.

"Are you cold? Are you running? Are you climbing a hill? What physical thing is your character going through? You also have to remember to have some emotional content to the performance. So you've got to ...basically remember to act or else you feel just stupid standing in the recording studio alone shouting ridiculous things," he said.

"You feel like an absolute idiot, so you've got to remember that this is silly, but it's still acting."

Monsters University opens in theatres Friday.