Michael Fassbender enjoyed his role as big-headed musician

“It was the maddest thing I’d ever read,” Michael Fassbender says of the screenplay for “Frank,” in which an aloof, avant-garde rock singer spends his entire waking life (perhaps his sleeping life, too) encased in a big, cartoonish, papier-mâché head.

“The whole story was so bizarre.… It was engaging and funny and had some really touching moments. How could I not do it?”

And so Fassbender — Magneto in the “X-Men: First Class” and “X-Men: Days of Future Past” and a supporting-actor Oscar nominee for his chilling turn as slave owner Edwin Epps in “12 Years a Slave” — agreed to try on the giant orb with the blank, sad visage, working opposite Domhnall Gleeson, Maggie Gyllenhaal and Scoot McNairy in the Lenny Abrahamson-directed film.

“It was actually pretty liberating to have the head on,” Fassbender says, on the phone from New York recently. “It made me concentrate on the physicality, how the body language might be amped up a little more — more awareness of expression through movement.

“But the rest of it was kind of fun. I could just play with my castmates and throw different things at them. It was like one of those trust exercises, where you fall backwards and you’re depending on the team to catch you before you hit the ground.”

The role of Frank, and the face of Frank, were inspired by real-life comedian-musician Chris Sievey, who introduced his spheroid-noggined alter ego, Frank Sidebottom, in the mid-1980s. Sievey, who toured as the character, died in 2010 from complications of cancer. Jon Ronson, one of the movies’ two writers, drew from his experiences playing in Sievey’s Oh Blimey Big Band. But as Fassbender notes, the film departs from Sievey’s concept.

“There’s one key thing — this anarchic streak to his character — that we’ve incorporated, but other than that, it’s very different,” says the actor. “Obviously, Chris Sievey was playing a character, but this Frank, our Frank, has a mental-health issue which the original guy did not. There’s a lot of damage in there, as it were.”

Fassbender has a handful of films coming up, including “Trespass Against Us, a tale of gypsy life set in the UK, opposite his “Frank” costar’s dad, Brendan Gleeson; “Slow West,” a 19th-century road movie teaming him with “The Road’s” Kodi Smit-McPhee; and “The Light Between Oceans,” based on the M.L. Stedman novel, with “The Place Beyond the Pines” Derek Cianfrance directing.

Then there’s an untitled Terrence Malick project, a film Fassbender made in Texas with the suddenly prolific “Tree of Life” auteur, just before shooting “Frank.” Christian Bale, Cate Blanchett, Ryan Gosling, Rooney Mara, and Natalie Portman are also said to be onboard.

“I don’t know if I’m allowed to talk about it,” Fassbender says of the film and its famously secretive director, who has been known to reshape movies in postproduction, leaving characters who seemed key in the screenplay on the cutting-room floor.

“I don’t know what the film is going to be — or if I’m actually in it,” he adds, laughing. “Not much help there, I’m afraid.”