The public loved Birdman. But Riggan Thomson, the actor who starred as the superhero in three hit movies, abandoned the character decades ago.

Turning his back on the franchise didn’t work out well for Thomson. Without the winged hero, the actor’s career plunged.

In the zealous comedy and drama “Birdman or The Unexpected Virtue of Ignorance,” Michael Keaton sweats bullets on Broadway as Thomson, a desperate man on a last-ditch quest for relevance.

The manic persona Keaton has applied to his comic characters through the years — Bill Blazejowski in “Night Shift,” for instance, and Betelgeuse in “Beetlejuice” — evolves naturally into “Birdman’s” actor on the ropes.

Keaton brings focus, immediacy, intensity to a performance that’s probably the best of his life. Some especially moving scenes achieve almost physical impact.

Hoping to reignite his free falling career, Thomson adapts a short story by Raymond Carver, “What We Talk About When We Talk About Love,” for the stage.

He’s also directing the production and starring in the lead role — a foolhardy quest, likely to fail and send him deeper in oblivion. With so much riding on the play, Thomson is grasping for what, at this late hour, must be a success.

To some degree, the fictional Thomson’s career parallels Keaton’s own film-star life. Keaton starred in 1989’s “Batman” and 1992’s “Batman Returns.” His films in the past decade include such unremarkable projects as “First Daughter” and “Herbie Fully Loaded.”

“Birdman” takes Keaton much higher. Fox Searchlight, the boutique studio that released the movie, is sure to stage a vigorous Oscar campaign for Keaton, his co-stars and the film’s stylistically distinctive director, Alejandro G. Iñárritu.

Although Thomson’s Keaton is the tortured centerpiece of the “Birdman” universe, the film is an ensemble piece. Leading the co-starring charge, Edward Norton blows into Thomson’s theater in the role of great Broadway actor Mike Shiner. A few days before the play’s opening night, Shiner pushes and inspires Thomson.

But Thomson, thrilled that the terrible actor who originally had Shiner’s part dropped out of the show, quickly sees that Shiner is a blessing and a curse. The men battle in explosive scenes, artistically and physically.

Shiner is recommended for the production by the play’s lead actress, Lesley. She’s also Shiner’s lover. That’s not going well either. “Birdman’s” well-written and well-acted characters continue with Naomi Watts and her performance as Lesley, a mature actress who, at long last, is making her Broadway debut. Like Thomson, the play could be Lesley’s last shot.

Zach Galifianakis, playing a dramatic role as Jake, Thomson’s producer, is another actor whose comedic skills make “Birdman” the often breathless, high-wire act it is.

Additional supporting characters include Laura (Andrea Riseborough), Thomson’s girlfriend and co-star in the play; Sam (Emma Stone), the actor’s daughter; and Sylvia (Amy Ryan), his ex-wife, bring some level-headedness to the cliff-hanging situation, even though Stone’s Sam is recently out of rehab.

Iñárritu, the first Mexican director to be nominated for an Oscar, previously helmed the jagged ensemble dramas “21 Grams” and “Babel.” With “Birdman” he narrows his focus to Thomson, a single character who, nevertheless, is of two warring minds. The film, gliding sans strings from hyper-real drama to lyrical magic realism, still looks and plays like the work of no other filmmaker.