Of all the memories shared by the three children of “Superman” actor Christopher Reeve, one immediately surfaces.

“Oh yes, that would be the ‘eject button,’” says Alexandra Reeve, 40, as her brother Matthew, 44, and half-brother Will, 32, both immediately smile.

The three gathered recently to discuss "Super/Man: The Christopher Reeve Story," a documentary about their actor-turned-advocate father (in select theaters; opens nationally Friday).

“Dad could control his wheelchair with one finger, and near that finger he had placed a sticker that said, ‘Eject,’” says Alexandra, laughing at the memory.

“Often you would see these congressmen and other important people he’d meet with thinking, ‘Wait, is that button for real?’” she says. “That sums him up to me. He loved playing with people.”

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Adds Will: “Yes, his feeling was, take life seriously, but don’t take yourself too seriously. That motto honestly could have been on the family crest.”

As its title cleverly suggests, ‘Super/Man” aims to deconstruct Reeve, who, thanks to his classic features and strong build, seemed to be the living embodiment of America’s storied cartoon superhero.

But the documentary, directed by Ian Bonhôte and Peter Ettedgui, digs deeper than the 1978 superhero role that ignited his fame, tackling Reeve's decision to leave the mother of his first two children, Gae Exton, as a result of personal demons; the paralyzing horse accident that should have killed him; and finally his transformation into a doting family man and disabilities champion.

By now, all three Reeve children have seen the documentary several times. They say the most trying part isn’t reliving the tragic moment when Reeve was thrown from his horse in a 1995 competition.

“The hardest thing, really, is us watching the interviews each of us did for the movie. So for me, it’s hard to see the moments where Will and Matthew choke up thinking about dad,” says Alexandra.

Matthew says that, as the oldest of the crew, he has many memories of his father well before the accident. But watching clips of his siblings “was tough, because you see what he meant to each of us, to our mom, to Dana (Will’s mother). Doing this ultimately was cathartic, in part because we three have gotten to spend more time together.”

Christopher Reeve inherited demons from his own demanding father

The movie plays like a parable of sorts. Pre-accident Reeve, while gregarious and fun-loving, is seen grappling with conflicting impulses and emotions that ultimately are resolved only after he is permanently confined to a wheelchair. (Reeve died in 2004; Dana Reeve died in 2006 from lung cancer.)

For example, there’s the divorce of Reeve’s parents that makes him vow to keep a stable household for his kids. And yet his youthful love affair with Exton, whom he met in London while filming “Superman” but never married, proves too confining and he bolts for the high life of mid-‘80s New York.

Reeve is determined to serve as a role model for his children. Yet he is constantly haunted by his impossible-to-please father, academic F. D. Reeve, which turns Christopher into the kind of dad who is always competing – whether in skiing, hockey, soccer or horse riding – with his offspring.

In one stirring moment in the film, Reeve, almost immobile in his wheelchair, says it took “breaking (his) neck” to finally grow truly close to his kids.

“The silver lining of his accident, you might say, is how it was a catalyst for dad and our family to never leave anything unsaid,” says Will, a correspondent for ABC News and "Good Morning America."

“The goal from then on was to share stories and feelings and hopes and dreams, to live a life that was open and honest, and yes, realistic, too,” he says. “The goal was us not feeling like we were being robbed of anything more than was already robbed by the accident.”

'Super/Man' features a trove of Christopher Reeve moments

Will Reeve says one joy of the documentary was seeing behind the scenes footage and home movies of his father in the heady years before his birth in 1992. A slim Reeve, then an unknown actor, bulks up at the gym for his breakout role, and cavorts with his longtime best friend, Robin Williams.

“I heard stories, of course, of this dynamic, adventurous, active man who couldn’t sit still, who rode horses and bikes and flew planes and skied, and while I didn’t experience that, I did see that same intensity and thirst for life in my dad after the accident,” he says.

Matthew's favorite moment is seeing an almost mischievous Reeve raise an eyebrow, smile and look deep into the camera, usually a home video recorder wielded by his doting wife, Dana.

"I can’t tell you how many times from across the room Dad would shoot me that same look,” says Matthew, growing quiet at the memory. “We shared that hundreds of times, that special father-son look.”

The moments in the documentary that had the greatest impact on Alexandra include two scenes in 1996, when Reeve rolled onto stages at the Oscars and the Democratic National Convention to deliver compassionate messages about the need for more funding for people with disabilities.

“He knew the day is not promised to any of us, and we need to reflect honestly about who we all are as people,” says Alexandra, who along with her siblings remains closely involved with the Christopher & Dana Reeve Foundation, focused on finding cures for spinal-cord injuries.

The Reeves, now adults with children of their own, are resolute that there have been only positive repercussions from sitting through countless interviews related to something that for any family would be considered a nightmare.

“This (documentary) is about showing a 360-degree view of an ordinary human who achieved extraordinary things,” says Will Reeve. “I’m prouder and prouder each time I watch it."