Peter Jackson’s “The Hobbit: An Unexpected Journey,” which opens Friday , is arguably the year’s most hyped and anticipated film. “The Hobbit” follows in the well-trod path of orc prints made by Jackson’s world-slaying “The Lord of the Rings.”

Before “Rings,” no one knew if Jackson’s cinematic version of J.R.R. Tolkien’s Middle-earth would have mass appeal beyond legions of existing Tolkien nerds. Yet, ever since the release of 2003’s “The Return of the King,” the final film in the cycle, fans have been waiting to bust down the gates back to Jackson’s vision.

“Middle-earth is a universe I know very well,” says Andy Serkis, who reprises his role as Gollum in “An Unexpected Journey,” and is also the film’s second-unit director. “Somewhere in the back of my mind I knew that Gollum wasn’t gone.” For him, since “The Lord of the Rings,” Gollum has been “absorbed into the public consciousness.”

Indeed, he and other Tolkien characters have haunted us for 75 years. Gollum, Gandalf, and Bilbo all got their start in “The Hobbit,” first published in 1937. The venerable children’s tale was the first of Tolkien’s works to creak open a round door into his rich legendarium about daring hobbits, gruff wizards, brash dwarves, and life-changing quests.

But with “An Unexpected Journey,” the first of a planned “Hobbit” trilogy, comes a dragon’s hoard of expectations, fears, and controversies. First, can Jackson weave his magic spell again, this time to transform a jovial kids’ book into mainstream adventure fare with more adult themes? The stakes are also high for financially feeble MGM, the film’s backer, which emerged from bankruptcy only two winters ago. And will a new batch of wizardly tricks enchant or turn off moviegoers?

Certainly, fans of “Rings” will be thrilled to see many of their favorite characters again, all played by the original actors. Ian McKellen returns as the cantankerous and mischievous wizard Gandalf, Cate Blanchett is back as the glimmering elf queen Galadriel, as is Hugo Weaving as the regal elf Lord Elrond, and Christopher Lee as the grim and conniving Saruman. Even “old” Bilbo (Ian Holm) and Frodo (Elijah Wood) make cameos.

But the core of “The Hobbit” cast, and plot, largely center around new heroes — a younger Bilbo, played by Martin Freeman (TV’s “The Office” and “Sherlock”) and the Company of 13 dwarves, headed by hunky Richard Armitage (“Captain America”) as Thorin Oakenshield. Together, Gandalf, Thorin, and his dwarves persuade a reluctant Bilbo to journey with them from the Shire into the wild, where they encounter trolls and goblins, dark caves, and riddle games. Their destination: the Lonely Mountain, where the dwarves must vanquish the evil dragon Smaug and reclaim their dwarvish homeland. The next two installments, “The Desolation of Smaug,” opening next December, and “There and Back Again,” slated for the summer of 2014, recount how well Bilbo and the dwarves fare on their quest.

Compared to the novel, the movie Bilbo is “not quite so inept,” says co-screenwriter Philippa Boyens, who also collaborated on the “Rings” scripts. “The truth is, he is very quick-witted. We just [portray] him being quick-witted a little bit earlier.” (Boyens, Serkis, and others from the cast and crew spoke via telephone from New York City and Wellington, New Zealand.)

Chief among the design challenges was to create individual looks for this baker’s dozen of dwarves. “We did over 800 illustrations and numerous sculptures in the search of 13 characters so that all would appear to come from the same race, some of them from the same family,” says Richard Taylor, co-owner and creative lead at Weta Workshop, the effects shop that made the swords, armor, prosthetics, and props for “The Hobbit” and “Rings.” The dwarves, he says, also needed to be “distinctly and uniquely different, all with their own iconic qualities so that, at a glance, the audience could tell them apart.”

As for the motion-captured, digital schizo Gollum, he’s about the same, says Serkis, albeit younger, since the action in “The Hobbit” occurs 60 years before “Rings.” His first day on the set, to film the “Riddles in the Dark” scene with costar Freeman, Serkis felt he was “doing an impersonation of other people’s impersonations” of Gollum.