NEW YORK —

Before he was a whiz of a wiz, if ever a wiz there was, the Wizard of Oz was Oscar Zoroaster Phadrig Isaac Norman Henkel Emmannuel Ambroise Diggs, late of Omaha. So it was said in “Dorothy and the Wizard in Oz,” the fourth of L. Frank Baum’s classic children’s books, and so it is now in Disney’s “Oz the Great and Powerful,” director Sam Raimi’s original prequel to the whole shebang. Like the novel and the musical “Wicked” did with the Wicked Witch of the West, the movie, opening today, means to fill us in on an iconic character’s back story.

Of course, given how beloved the 1939 movie musical “The Wizard of Oz” is, Raimi naturally worried some people would take him for a humbug.

“When it was offered to me,” the “Spider-Man” and “Evil Dead” director said of the initial script, written by Mitchell Kapner, “I didn’t exactly want to read it because I was such a big fan of ‘The Wizard of Oz,’ and I thought perhaps it would tread upon the great good name of that classic film. And I thought maybe fans would be upset if you made a prequel. But a number of weeks later, I was working on another project and I was looking for a writer, and this was handed to me as a writing sample.”

He gave it a read, he said by phone from Los Angeles, “and I thought this actually could be a very uplifting picture.”

It certainly uplifts the once and future wizard (James Franco): In a sequence that echoes Baum’s description, circus performer Oscar — a ventriloquist in the books, a magician in the movie — finds himself in a hot air balloon lifted by a cyclone taking him somewhere over the rainbow. The film fills in that Oscar, nicknamed Oz, left behind the Baum Bros. circus, where he performed with faithful assistant Frank (Zach Braff). It also gives us Annie (Michelle Williams), whom he loves but for whom huckster Oz feels he’s not good enough.

Yet after reaching the magical land whose name he shares, he meets her look-alike, Glinda, along with her fellow witches Evanora (Rachel Weisz) and Theodora (Mila Kunis). He also finds a new faithful assistant in winged monkey Finley (voice of Braff) and a surrogate daughter in the porcelain China Girl (voice of Joey King).

Raimi, after working with Kapner on a new draft, summoned Pulitzer Prize-winner David Lindsay-Abaire (“Rabbit Hole”) for two more. Production on the reported $200-million movie commenced in July 2011 at what was then the Raleigh Michigan Studios in Pontiac, Mich., not far from the Detroit suburb of Royal Oak where Raimi grew up. Though Disney had wanted to shoot in slightly more cost-effective Vancouver, the director wanted to help his home state’s film industry, he said. “I begged Disney to let it go there, and they were very kind to let me do that.”

Like Lindsay-Abaire, the formidable Franco — an Academy Award-nominee for “127 Hours” (2010) — also wasn’t originally attached to the film: Robert Downey Jr. and Johnny Depp had been in negotiations first to play Oz. “I didn’t mind at all, especially because those are two of the biggest actors around,” said a sanguine Franco. “They’re great at playing leading men that have comedic sides to them. You could almost say that they’re the masters of that. And so I was not surprised or offended at all that Disney or Sam went to those guys before me.”

And Franco, importantly, brought improv experience honed by working with filmmaker Judd Apatow and actor Seth Rogen, which helped ease him into a Hope-and-Crosby rhythm with quick-witted co-star Braff.

“When I met Sam, he said he wanted me to improv and come up with jokes in addition to being just the monkey’s voice,” the former “Scrubs” star said. He told Raimi, “Are you sure? All we did on ‘Scrubs’ for nine years was riff jokes, so I’m going to be like a fire hose coming at you. You have to promise you’re going to tell me when you want me to shut up.”

Raimi gave him rein, he said happily. “There were times, though, when I pitched some elaborate tangent, and he’d be laughing and like, ‘Alright, that would be hilarious if the movie were called “The Monkey,” but it’s called “Oz” so let’s tiptoe back to the script.’”

Baum, who wrote the first 14 Oz books, wasn’t averse to spinoffs, authoring Oz plays, movies and other media. After his death in 1919 came many more novels by other writers — in and out of canon, estate-authorized and not. There have been Oz comics, video games, even slot machines. And while not all of these, perhaps, were labors of love, “Oz the Great and Powerful” is clearly so.

“I love the Judy Garland film, but I also read all the books when I was a boy,” said Franco. “Oz has had a big place in my life for a long time.” And the movie’s retroactive continuity felt right to him. “I loved their idea of the character, that he was not an innocent like Dorothy going to this world, that he was anything but, so his experience of Oz would be completely fresh, and miles away from Dorothy’s.”

We aren’t in the old Kansas, Toto

Glinda still travels by bubble. Sleepy-time poppies? Got ’em. “Oz the Great and Powerful,” a Disney-made prequel to “The Wizard of Oz,” even begins in black and white and then switches to plush color.

But there are also some important differences between the two movies — especially if you’re an eagle-eyed Hollywood copyright lawyer.

‘Yellow brick road’

It unfurls in full glory, but there is minimal skipping down it — this is not a musical — and Disney, concerned about copyright, does not show it spiraling into the same stylized point in Munchkin Country. (Munchkinland was an invention of the 1939 film.) But Sam Raimi added a twist of his own: His road changes moods.

‘RUBY SLIPPERS’

Since this is a prequel — the wizard’s story — Dorothy doesn’t appear. Ditto her famous footwear. Raimi couldn’t have adopted that fashion statement anyway. The slippers were silver in the books; it was the 1939 film, eager to show off Technicolor’s magic, that made them ruby.

‘WINGED MONKEYS’

The witch’s flying henchmen have become sharp-toothed baboons in Raimi’s movie. There is also a new character, Finley, a friendly flying monkey in a bellhop uniform.

‘MUNCHKINS’

About 40 dwarfs were cast in “Oz the Great and Powerful” as Munchkins. However, their characters are more ethnically diverse than in the original.

‘WICKED WITCH OF THE WEST’

Striving for a visage different from the one Margaret Hamilton made famous, Howard Berger, an Oscar-winning makeup artist, created a new green that he named his custom color Theostein — a conflation of the witch’s name before she turns wicked, and Frankenstein.

— New York Times News Service