Eric McCormack has come a long way since his early days in the acting business.

Between years at theater school, McCormack, then 20, played the Kool-Aid man, and not in a commercial. He actually dressed up in the Kool-Aid mascot's recognizable costume.

"And I would walk around and kids - you'd think they'd have a lot of affection for the big red jug. No, it was very violent," McCormack, now 50, told "Good Morning America" correspondent Amy Robach in an interview that aired Monday on the show. "They wanted to push and punch and knock me down."

WATCH: Eric McCormack's New Role in 'Perception'

McCormack, who went on to play William Truman in the hit sitcom "Will & Grace," has another hit show on his hands.

In the TNT drama "Perception," McCormack plays Daniel Pierce, an eccentric neuroscience professor and paranoid schizophrenic who is recruited by the FBI to help solve complex cases.

He said he did his homework to prepare for this role. It was important, "particularly you want to be able to go to the mental illness community and say 'I'm not taking this lightly … we're approaching this with accuracy and with empathy,'" he said.

As part of his research, he read about Elyn Saks, a professor of law and psychiatry at the University of Southern California, who wrote "The Center Cannot Hold: My Journey Through Madness." The book details' Saks own experiences suffering from schizophrenia.

"She wrote a book about, actually, losing her mind in the '70s and how that felt and what hallucinations feel like and voices. So she was probably my model as I started the process," he said.

"Perception" is now in its second season.

He said it's interesting to go from "Will & Grace" to "Perception." The sitcom made its mark for bringing gay characters and themes to the mainstream, and he said he hopes to have a similar effect on the mental illness debate through "Perception."

"It's sort of the last taboo in a lot of ways, in terms of what people are willing to face," he said.