He’s a comedy legend, one of the greats. But does anyone really know Steve Martin?

Later on — after conquering Hollywood as a charming and family-friendly leading man — Martin emerged in print as the kind of wry prankster whose jokes were so subtle you had to be careful not to miss them — the wild and crazy guy reinvented as a distinguished man of letters.

In other words, Steve Martin contains multitudes, and Oscar-winning documentarian Morgan Neville’s new film about his life and work has been carefully structured to reflect this duality. As per its subtitle, Neville’s three-hour portrait “STEVE! (martin)” is a documentary in two pieces, each edited as their own stand-alone feature.

The first part focuses on Martin’s early life and rise to celebrity while the second catches up with him in the present tense; each instalment has its own visual style and narrative arc. In theory, you could watch one without the other and still come away with a more intimate knowledge of an iconic American comedian; taken together, in either order, they comprise a genuine epic about a worthy — and surprisingly willing — subject. The doc premieres on Apple TV Plus on Friday.

“Everything about Steve, to me, works on multiple levels,” said Neville via a Zoom interview with Martin and the Star.

“His standup played to an eight-year-old kid but also to my dad, who was sophisticated. High culture and low culture; the very obvious and the very subtle.”

Neville explained that while he didn’t set out to make two separate movies about Martin, the bifurcation happened naturally. “I felt like there were two very different stories. One was about somebody’s solitary journey to find his artistic voice; the other was about somebody whose life and work branch off in a lot of different directions.”

“I actually didn’t know there were two different crews who weren’t interacting with each other,” added Martin in his familiar chipper deadpan. “But there were people combing through my house forensically like I’d murdered somebody.”

One thing that’s clear watching “STEVE” is that Martin’s well-practised public persona — the benign, smiling egomania on display when he hosts awards shows or pops to cameo on “Saturday Night Live” — is as much a creation as the heroes of “The Jerk” or “Roxanne.” 

One of the film’s key themes is its subject’s long-standing ambivalence — bordering on antipathy — to being examined or interviewed. The archival clips compiled by Neville and his editors capture the difference between his complete self-assurance onstage and his frustration when somebody else is holding the microphone.

“With a documentary, you think ‘I won’t have to go do interviews about it,’” smiled Martin when asked if he enjoys doing press and promotion more now than at the height of his fame. “I’ve just been in a movie (about myself) that’s over two hours long and now I’m talking about myself.”

What’s fascinating, especially in the doc’s second part, is how thoroughly Martin’s prickliness melts away — a testament to Neville’s intimate but respectful approach, but also seismic shifts in his life including marriage and fatherhood, and a diversification of his artistic practice toward collaboration.

If Part 1 suggests an iconoclast driven by loneliness, Part 2 shows Martin surrounded by friends, peers and loved ones.

“I remember when I hosted ‘Saturday Night Live’ in 1976 and I had just been doing standup my whole life,” said Martin. “I was out there doing a sketch and there was like there was a thought balloon above my head, and it said: ‘Other people?’ But I love working with other people.”

“The honesty I saw in Steve’s memoir ‘Born Standing Up’ told me that he was capable of introspection and of understanding things about himself,” said Neville. “I didn’t know what the movie was going to be; we got together with a tape recorder and sat down (and) I got to see what he was willing to talk about. Like, there’s a clip in the movie where somebody asks him about his art collection and he says he won’t talk about it, and now he does.

“We have an interview where Adam Gopnik from the New Yorker (that) says that Steve’s changed more than anybody else he knows, and I wanted to understand that.”

There is a sense in which parts of “STEVE” are treading familiar territory: Part 1 draws significantly from “Born Standing Up,” which, among other things, is a great disquisition on the metaphysics of comedy. Watching the young Martin experimenting with his deceptively earnest stage persona — the faux-folksy patter, the barely sublimated contempt, the almost subliminal play with language and rhetoric — is almost clinical.

He says that he still stands by some of the theories he cultivated in his salad days, especially the idea that nothing is funnier than making people wonder whether or not something was supposed to be funny.

“There’s something I’ve learned through the years about withholding,” he explained. “If the audience is laughing and they don’t know why, it’s the greatest laugh of all. When funny is in the air, there doesn’t need to be a punchline all the time.”

For Neville, Martin is the kind of comedian who’s sometimes so ahead of the curve that he seems out of step. “The culture has to catch up to him,” he said, citing 1981’s widely panned — and commercially DOA — musical “Pennies From Heaven” as Exhibit A.

The film, directed by Dennis Potter, was a delicate, expressionistic musical set in the 1930s during the Great Depression, and Martin was pilloried for trying to shift gears from more crowd-pleasing farces. “When I made it, I sort of knew that it would be seen as ‘the followup’ to ‘The Jerk,’” said Martin. “But I also knew that one day, it would just be a movie and I’m interested that it’s been reclaimed.”

What’s beguiling about “Pennies From Heaven” is its melancholy, and “STEVE” doesn’t shy away from exploring the pathos of Martin’s work, which is partially rooted in difficult childhood memories of his father and also a more existential sort of angst that poked through even his goofiest routines (“we’ve had some fun tonight, considering that we’re all going to die someday”). But the prevailing sensation in the second part is one of palpable and enviable fulfilment: the byproduct of a condition that Martin refers to onscreen as a “relaxed brain.”

“You go from thinking ‘It’s all going to be over in a minute’ to ‘I’m still here,’” said Martin. “It’s a good feeling.”

“STEVE! (martin) a documentary in two pieces” premieres on Apple TV Plus on March 29.