The great ones are all raving egomaniacs. Their focus and commitment are next level intense, and that intensity is all focused on them. Their egos are generally unchecked, fame and glory are birthrights, their narcissism a badge of honor.

Being in the presence of the famed swimmer, sportscaster, #MeToo activist so early in the fight she could rename it #MeFirst, Diana Nyad has to be a little like listening to Pavarotti warming up backstage.

“Me me me me me me MEEEEEeee!”

That’s the obnoxious-to-the-point-of-adorable portrait of Nyad that Annette Bening gives us in “Nyad,” a grueling, amusing and eventually inspiring bio-pic about the greatest long distance swimmer of them all, and Nyad’s great white whale — her unshakeable determination to be the first to swim from Cuba to Florida through the treacherous Florida Strait.

“Nyad” blends TV news coverage of the marathon swimmer’s various epic swims and attempts at her longest — the Havana-Key West quest — with sometimes uplifting, sometimes grim childhood flashbacks and fun and fiesty scenes of the unbearable bore she (Bening) is at 60, raging about “mediocrity” and “laziness” and, it is implied, the lack of a spotlight shining on her.

“I don’t believe in imposed limitations,” she sermonizes to her long-suffering friend-not-lover and audience-of-one, Bonnie Stoll (Jodie Foster). Don’t talk about her age. Don’t let her think she’s just another woman over 60, silenced by the culture and left “waiting to die.”

Spurred by a book of poetry she comes across by Mary Oliver, Nyad takes Oliver’s most famous line as a credo, a challenge, a call to (getting her swimmer’s) arms back in shape.

“Tell me, what is it you plan to do with your one wild and precious life?”

Bonnie, an ex-athlete herself , has to listen to this endless monologue of on-the-spectrum narcissism — again, great singers, actors and especially athletes are often like this — and when her closest friend decides to renew her greatest challenge thirty years after her “last swim” attempt to conquer it failed, Bonnie has to be there.

“Free Solo” co-directors Jimmy Chin and Elizabeth Chai Vasarhelyi transition from documentaries to feature films with a sports bio-pic that checks off many of the genre boxe — the obstacles, moments of truth that will test our plucky and amusingly unbearable heroine, the tragedy that enters the picture, the full “thrill of victory, agony of defeat” experience that Nyad used to chronicle herself during her years with ABC’s “Wide World of Sports.”

The tests of her childhood include abuse, and implied abandonment issues.

Where the filmmakers score is in the casting. Bening, perhaps sensing an Oscar nomination in the role, lets us see her at Nyad at her insufferable worst, and Bening herself at her least glamous no makeup, swimsuited and fit enough but AARP-aged in every moment. Her form in the water is impressive enough for us to make the buy-in, her depiction of Nyad so fearlessly unlikable that you have to wonder if they’re on speaking terms.

Foster’s Bonnie is the audience’s surrogate, the one who endures Nyad’s endless versions of her “You’re named for a water nymph” speech from her adoptive (Greco-Egyptian) dad, who suffers through all the training and attempts Nyad would make in her 60s what she couldn’t manage in her late 20s.

We wait for Bonnie to protest, punch back or just demand that her closest friend dial back her “superiority complex” just a tad. Foster, her luminous screen presence undimmed, makes Bonnie the fabric softener to Bening/Nyad’s abrasive wet wool performance. Loved Bening. Foster is who makes “Nyad” bearable.

Ryhs Ifans comes on as the crusty Florida Keys “navigator,” “The King of the Gulf” who would chart a path and track the shifting currents of the Florida Strait, while others would figure out solutions to the sharks and killer jellyfish that awaited our intrepid swimmer as she tried to put in her 250,000 strokes, covering 103 or so miles, singing pop hits of her youth to herself to pace that voyage.

I kept thinking of that obnoxious Millenial put-down, “Okay, Boomer” during “Nyad,” because living in Florida and having sailed the Florida Strait, one remembers the many attempts, the needy-seeming media attention and maybe even feeling “Oh, give it up, sister” at all the self-aggrandizing hooplah.

And yet, she persisted.

Maybe it’s the ultimate “Boomer” picture. But if you can’t connect to her story or that megaphone Nyad kept raising to her lips as she raged, raged “against the dying of the light,” you will. Just give it time.

Rating: PG-13, peril, some nudity, profanity

Cast: Annette Bening, Jodie Foster and Rhys Ifans.

Credits: Directed by Jimmy Chin and Elizabeth Chai Vasarhelyi, scripted by Julia Cox, based on Diana Nyad’s (4) memoirs and other writings and public pronouncements. A Netflix (theatrical first) release.

Running time: 2:01