Repeated filming delays almost caused Ian McKellen to quit his reprise as Gandalf the Grey in “The Hobbit” trilogy, a prequel to “The Lord of the Rings” in which he first played the wily wizard.

“It wasn’t a simple offer,” he said, recalling that in the two years since he first accepted the role, Peter Jackson pulled out as director, then replacement Guillermo del Toro dropped out, followed by Jackson becoming ill after he signed on again. “I just had to keep adjusting to the possibility that the film was never going to get made.”

But McKellen decided he “must do it” for both the fans and himself, despite his various doubts about returning to the role. And he says any concerns he had about bringing Gandalf back to life vanished as soon as he slipped back into those wizardly robes — along with the beard, mustache and fake nose.

“That was the moment when I thought, ‘Oh, it’s all right. I do still remember the old boy,”’ the actor recalled in a recent interview to promote “The Hobbit: An Unexpected Journey,” which opens in North American today. “The voice came back and there we were. It was a very quick, easy thing to do.”

Not so easy was adapting the technicalities needed to re-create Middle Earth and all of its characters of various shapes and sizes. Because Gandalf is larger than most of the other “Hobbit” characters, including its 13 dwarves, McKellen often filmed by himself in front of a green screen, which he called “frustrating.”

“It does mean that I’m talking to 13 people that aren’t really there, whose voices I can only hear through an earpiece,” he said. “That’s not really comfortable and doesn’t leave a lot of room for spontaneity.”

Some reviewers have criticized “The Hobbit” for drawing out the original story, adding characters and taking oblique references from “The Lord of the Rings” appendices to create tension and a bad guy.

However, McKellen says he believes Jackson stuck to J.R.R. Tolkien’s vision. “I think Peter has genuinely found a method of adding images to Tolkien’s amazing words, which are the pictorial equivalent to the words,” and embedded them into his “filmmaking innards.”

Jackson would not do anything to “contradict Tolkien’s intentions of even his methods of storytelling,” McKellen said.