In the middle of training for his big comeback, the world's greatest basketball player switched between sweaty practice drills and conversations with a cartoon rabbit.

The result of that balancing act - “Space Jam” - opened 20 years ago Tuesday. Looking back on the movie starring Michael Jordan and the Looney Tunes gang now, few would have guessed its enduring appeal: Part animation, part live action, this alternate explanation of Jordan's retirement involves a basketball game against cartoon aliens, the Monstars. Other pro players - Patrick Ewing, Muggsy Bogues, Charles Barkley - make prominent cameos. Bill Murray's there, too, for some reason.

Technologically impressive at the time, “Space Jam” has become a sort of nostalgic, cultural phenomenon. Grown adults wear “Space Jam” basketball jerseys and pore over the movie's website (which, yes, is still online in its original form). There are dedicated subreddits for remixes of the soundtrack, and anticipation over a sequel (rumored to be in the works). Nike plans to reissue its namesake shoe. Anniversary screenings hit theaters nationwide this week.

When the movie first came out, most critics panned it, but Roger Ebert wrote it's “a happy marriage of good ideas - three films for the price of one.”

The public agreed with him: The movie earned more than $90 million at the domestic box office and $230 million worldwide. Merchandising brought in more than $1 billion in retail sales. “Space Jam” remains the highest-grossing basketball movie of all time.

Pairing Jordan with Looney Tunes characters originated with the Nike “Hare Jordan” ad campaign. Jim Riswold, then creative director and partner at Wieden+Kennedy, helped develop the concept after working on the popular commercials that paired Jordan with Spike Lee playing the character Mars Blackmon.

“They wanted to do something different for the Super Bowl, so I couldn't think of a greater star than Bugs Bunny to put him with,” Riswold recalled. Bugs Bunny was the exec's “childhood hero.”

The pairing was practical, too.

“To be honest, a lot of athletes aren't good actors because they have better things to do: be good athletes,” he said. “You put someone up with them to do the talking. Mars Blackmon and Bugs Bunny can both talk the balls off a statue.”

Warner Bros. was excited at having one of their licensed properties involved with Jordan, but was anxious over how Bugs would be portrayed. “I wanted to use the Bugs Bunny from the '40s, which is not very P.C.” That Bugs would blow stuff up with dynamite, and “there's certain things they didn't think Bugs should do anymore.”

The resulting ad, in which Bugs and Jordan defeat bad guys on the court, took about six months to make and cost an estimated $1 million, Nike execs said at the time.

“Hare Jordan” was the Super Bowl's most talked-about spot in 1992. “This could be the beginning of a beautiful friendship,” Bugs quips at the end, and it was; another “Hare Jordan” commercial followed.

The popularity proved the duo had legs. But a Jordan movie? His longtime manager, David Falk, said Jordan “had been offered dozens of movie roles over the years, and we turned them all down.”

“I always used to tell him when we'd turn the deals down, 'You can't act. There is only one role for you,' ” he added.

Jordan, “a tremendous prankster,” would joke back: “The first black James Bond?” No, Falk responded. Michael Jordan.

So the impetus for “Space Jam,” Falk said, was for “Michael to play himself.”

By the mid-'90s, Jordan had become an international icon. Together with Ken Ross (now a CBS executive), Falk pitched a Jordan movie to the major studios. The idea wasn't fully formed - the script and exact story would be developed later.

It wasn't an instant sell. Dan Romanelli, who ran Warner Bros.'s consumer products division, got a call from Falk, who said Warner Bros. had “turned down an opportunity to do a movie that was with Bugs Bunny, the Looney Tunes,” Romanelli recalled. He responded: “That's impossible. How can you not do something with Michael Jordan?”

Romanelli also saw the enormous retail potential (like Daffy Duck seeing dollar signs). Such a project would mean plush toys and action figures. “I've been wrong about other things, but I felt like with Michael, you just can't go wrong. He's gold,” Romanelli said.

He faced some skeptics who didn't think it could work.

Lucy Fisher, Warner Bros. executive vice president of production, said, “They didn't really want to mess around with Bugs unless there was some good reason to, and it just seemed too hard.” But she believed in it. “Dan showed me the commercial, and then as soon as I saw it, I said, 'I see the whole movie. I don't know what the story is, but the dynamics are fantastic.' ”

Fisher was a big fan of Jordan, not basketball. Seeing the movie's potential among people who didn't care much about sports, she advocated for the movie, which Warner Bros. chief executive Bob Daly then enthusiastically green-lighted.

“I used to say, the two biggest stars we had at Warner Bros. were Clint Eastwood and Bugs Bunny,” Daly said.

They hired Joe Pytka, who directed the “Hare Jordan” ads and had a good rapport with Jordan. Ivan Reitman joined as producer, and his team came up with the concept of Jordan helping the Looney Tunes in a basketball game against the Monstars, Fisher said.

In the middle of all this, Jordan announced his retirement and began playing baseball. That complicated matters. “We said, 'Let's just write it into the script,'” Fisher recalled.

By summer 1995, Jordan was training for his comeback to basketball. Warner Bros. built him a gym on set, per his contract. “Just the air-conditioning for the court was really expensive,” Falk recalled.

Actors, executives and others on the lot would show up to watch Jordan's pickup games.

“Every day in between shots, he would go practice. And every night, he'd usually bring in some pros in the area, or college kids, and they'd play basketball,” Daly said. “That's when I realized the unbelievable dedication he had to coming back.”

Reitman had directed a bunch of Bill Murray's hit movies, but on set, folks weren't sure whether Murray would show up for his handful of shooting days.

“Everybody wanted him, and Bill Murray is notoriously elusive,” Fisher said. “It was one of those things, up until the last minute, whether he would say yes or no - I think we had some backup plan.”

In the beginning of the movie, when Murray asks Jordan why there's no room in the NBA for a guy like him, he adds, “It's 'cause I'm white, isn't it?”

“No. Larry's white,” answers Jordan, referring to Larry Bird (also in the movie).

“Larry's not white,” Murray improvised. “Larry's clear.”

“Space Jam” also had plenty of product placement, years before it became the industry norm. Jordan blazed marketing trails. Gatorade and Wheaties and his other sponsored products are mentioned in the movie. “Everything he did was integrated,” Falk said.

Ross developed the soundtrack, which was instrumental in the movie's success and lasting appeal. R. Kelly's “I Believe I Can Fly” won a Grammy and “Fly Like an Eagle” became one of Seal's biggest hits. People still remix Quad City DJ's title track.

The movie promotion included a dedicated website - cutting-edge stuff in 1996. Don Buckley, then-Warner Bros. vice president for advertising and publicity, had built sites for “Batman Forever” and “Twister” before the Jordan project.

“We were deadly serious about how important the internet was going to become,” Buckley said of his website-building team. But they also inserted jokes into the source coding, and some elements of the site were written “in this kind of wise-ass New York, almost Bugs Bunny-esqe style,” Buckley said.

Unimaginable today, but a movie with an $80 million budget had a marketing component characterized by a renegade quality. “No one was looking over our shoulders,” Buckley recalled. “We kind of did what we wanted.”

Rolling Stone recently published a history of the still-live website. Despite a look that's primitive by today's standards, a recent meme noted its similarity to the Apple Watch home screen.

“It's an artifact today,” Buckley said. “The fascination people have with that website is really evidence of their love and appreciation with the film itself.”

The website describes how the movie was made. Elements of the animation were done by hand before computers got involved, as 150 animators worked on the movie. Cinesite, which worked on “Who Framed Roger Rabbit” - the 1988 pioneer of the live-action/animation mashup - then combined the worlds.

Jordan filmed over six weeks, acting alongside members of the Groundlings improv theater.

“It'd be hard to say he had fun,” Falk said of Jordan. “It was an interesting experience, but doing six weeks of green screen was grueling.”

Jordan did like “the camaraderie of doing it with a bunch of his friends,” Falk added. But when a sequel was offered, he turned it down.

Romanelli, the Warner Bros. marketing executive, said pushing the movie through was “one of my proudest moments” at the company. And he had been right; “Space Jam” branded jackets, jerseys, action figures and towels hit the market, bringing in more than $1 billion in retail sales.

“I remember one of the international executives said he thought we were very lucky with that,” Romanelli recalled. “Luck had nothing to do with it. It all had to do with Michael Jordan and the Looney Tunes, and a really fun, sweet story that resonated with fans all around the world.”

After its box office success, Warner Bros. tried more animated feature films. Those immediate efforts flopped.

“We got spoiled by doing 'Space Jam,'” Daly, the former chief executive, said. “ 'Space Jam' came too easy and became too successful too fast, and we thought, 'Oh, why not go into the animation business?' ”

Riswold, the ad man who helped come up with the Bugs-Jordan pairing, wasn't a fan of “Space Jam.” He calls himself a purist; the Bugs on the big screen just wasn't the one he remembered from his childhood. “It's a marketing idea first, and a movie, maybe ninth.”

But, he added, “That's OK. It made a lot of people smile, and we all know the world could use more smiling.”