“Wicked” author Gregory Maguire, who now lives in the Boston area, has been re-imagining the story of “The Wizard of Oz” since he was a child.

“I was the middle kid, for one thing. But I was also the idea man,” he told GBH’s Morning Edition co-host Jeremy Siegel. “So when little kids had to be babysat, I was young enough to be forced to do it. And I was old enough to have ideas for what to do next.”

He would wrangle his siblings into his own productions of “The Wizard of Oz,” L. Frank Baum’s fish-out-of-water tale of adventure and friendship. And after a while, he started to remix the story.

He tried gender-bending his casting and inserting characters from other stories, like Peter Pan’s Captain Hook.

“You add just one new element to what you already knew, and the story cannot end the way that it used to,” he said.

His 1995 book “Wicked” — a retelling of L. Frank Baum's classic Oz through the eyes of the Wicked Witch of the West, who he named Elphaba — has been turned into a wildly successful Broadway musical and, later this year, a film adaptation starring Ariana Grande as Glinda and Cynthia Erivo as Elphaba.

“In a way, my ability to write stories was a result of my ability to play like any child's ability to play, to take what you have and make something new out of it,” he said. “If that doesn't work, take it again, scramble it up and make something new again.”

The Wicked Witch of the West doesn't have a name in the original tellings of “The Wizard of Oz,” either the Baum books and their film adaptations. That's something Maguire said he wanted to change.

“I invented the name by playing with the initials of the author, Lyman Frank Baum,” he said. “I tried Lafaba, I tried Lafeyba. And then I tried Elphaba. As soon as I got Elphaba, I thought, oh, that's it.”

When he first saw "The Wizard of Oz" as a little kid, the witch for him was a nameless terror.

“I was terrified of her. And I was also scared, of course, of the flying monkeys,” he said. “But by the time I'd seen the show maybe five times ... I began to realize that the wizard, who lied to Dorothy — who sent her off into danger with no expectation of being able to pay his debt to her — was just as scary, if not, in fact, scarier.”

Exploring the story from Elphaba’s perspective began with Maguire “ingesting and digesting” what the story was saying about structures of power, he said.

“The witch? Yeah, you know, she's menacing to my dreams still,” Maguire said. “But she never lied to Dorothy. She never tried to trick her. She said exactly what she felt. And she did exactly what she said she was going to do.”

Three decades later, "Wicked" is now synonymous with musical theater after the adaptation's smashing success on Broadway. Come November of this year, it's all but certain to be a blockbuster film, too.

But despite being the wizard of words behind it all, Maguire said at this point his world of Oz has largely become a world of its own.

He got to go to Elstree Studios in Borehamwood, north of London, to watch about five days of filming for the upcoming movie.

“What I can speak about with alacrity and passion is how much I learned about the art of acting by watching Cynthia Erivo, Ariana Grande and Jonathan Bailey,” he said. “I was amazed at the capacity of people that I think of primarily as singers to be as talented and as precise and as intellectual in their approach to the reading of a scene as they are to the shaping of a melodic line, let's say. It was mind-boggling for me, whose mind likes not to be boggled.”

When a trailer for the film adaptation aired during this year’s Super Bowl, Maguire said, he wasn’t even watching. He had no idea it was coming.

“Everybody else in the world saw it before I did,” he said. “But the next morning my media, as they say, 'blew up' and I went and found it.”