Margot Robbie and Cillian Murphy — she the star of “Barbie,” he of “Oppenheimer” — have shared an experience, one unique in film history. On July 21, 2023, their two movies came out, and instead of cannibalizing one another during a time when box office receipts were sluggish, they actually boosted each other, creating the global phenomenon known as “Barbenheimer.”

On paper, the two movies couldn’t be more different. Greta Gerwig’s “Barbie,” produced by Robbie’s company LuckyChap Entertainment, is the story of the world’s most popular doll, who, after going on a journey to recover from an existential crisis, becomes a woman; Christopher Nolan’s “Oppenheimer” is a biopic about J. Robert Oppenheimer, the physicist who oversaw the invention of the atomic bomb. What they have in common, though, is that their directors made wholly original films, ones guided by their inventiveness, and it was the innovative spirit of “Oppenheimer” and “Barbie” that in turn inspired audiences to be creative and participatory in their fandom for both films.

The memes, the double-feature TikToks, the costumes people wore to go out to theaters again and again to experience Barbenheimer — after COVID had nearly destroyed in-person moviegoing — “Barbie” and “Oppenheimer” proved joy is still to be had (as well as profits, with the box office for “Barbie” at more than $1.4 billion worldwide, and “Oppenheimer” recently crossing $950 million).

In other words, Robbie, sporting a “Barbie”-inspired pink polka-dot shirt with matching heels, and a darkly clad Murphy have a lot to discuss when they meet for Actors on Actors — a rendezvous during which Murphy professes he now knows what a meme is, after famously claiming ignorance about them in a 2017 interview.

Alexi Lubomirski for Variety

CILLIAN MURPHY: Congratulations on your reasonably successful film. You’re a producer on the movie as well. How did you know a “Barbie” movie would connect with audiences in the manner that it did?

MARGOT ROBBIE: Yeah, 90% of me was certain that this would be a big deal and a massive hit, and 10% of me thought, “Oh, this could go so badly wrong.” It was all about Greta Gerwig. And it was like, “If it wasn’t going to be Greta, then, yeah, this could have been an absolute disaster.”

MURPHY: She was always your first choice?

ROBBIE: I just wasn’t going to let her say no. It was about six years ago we got the property. We got it out of Sony, set it up at Warner Bros., got Mattel’s blessing to let us produce, then went after Greta. Obviously, I didn’t know it was going to be the cultural phenomenon that it ended up being.

MURPHY: When did you realize that?

ROBBIE: It was all the way along. The fact that it’s Greta Gerwig, people are like, “Greta Gerwig and a ‘Barbie’ movie, what?” And then the pictures of Ryan Gosling and me Rollerblading on Venice Beach came out and went even wider than I was expecting. I’d been thinking big for it, and it still turned out bigger than I expected.

But what about you? Did you think so many people were going to watch a movie about the making of the atomic bomb?

MURPHY: No. I don’t think any of us did. Christopher Nolan was always determined that it would be released in the summer as a big tentpole movie. That was always his plan. And he has this superstition around that date, the 21st.

ROBBIE: Do all his movies come out on that date?

MURPHY: In and around the 21st of July — they always come out then.

ROBBIE: It’s a good date. We picked that day too!

MURPHY: Yeah, I know.

Alexi Lubomirski for Variety

ROBBIE: One of your producers, Chuck Roven, called me, because we worked together on some other projects. And he was like, “I think you guys should move your date.” And I was like, “We’re not moving our date. If you’re scared to be up against us, then you move your date.” And he’s like, “We’re not moving our date. I just think it’d be better for you to move.” And I was like, “We’re not moving!” I think this is a really great pairing, actually. It’s a perfect double billing, “Oppenheimer” and “Barbie.”

MURPHY: That was a good instinct.

ROBBIE: Clearly the world agreed. Thank God. The fact that people were going and being like, “Oh, watch ‘Oppenheimer’ first, then ‘Barbie.’” I was like, “See? People like everything.” People are weird.

MURPHY: And they don’t like being told what to do. They will decide, and they will generate the interest themselves.

ROBBIE: I think they were also really excited by the filmmakers. People were itching for the next Chris Nolan film and itching for the next Greta Gerwig film. To get them at the same time was exciting. You’ve done five movies with Christopher Nolan now, right?

MURPHY: This is six, actually.

ROBBIE: So you like the guy? A big fan.

MURPHY: It seems to work. This is the first time playing a proper lead role for him. There’d always been supporting parts over the years — it’s 20 years we’re working together. Emma Thomas, his wife, the producer, she called me because Chris doesn’t have a phone. So she put me on to Chris, and he said in his very understated British way, “I’m making this movie of Oppenheimer — I’d like you to play the part.”

I had just finished something; I wasn’t doing anything. I did realize then that it was different than the other jobs I’d done with him, because it was the story of Oppenheimer’s life. And then when he eventually gave me the script, it was written in the first person, which I’d never read before, and so I —

ROBBIE: The script was written in the first person? The big print would be like, “I’m going to put the cup down and walk towards the door”?

MURPHY: Exactly, exactly. Which I’d never read before. And so it was very clear that he wanted it to be truly subjective storytelling. And that did add to the feeling of “Oh, fuck, this is a biggie.”

ROBBIE: Why do you love working with him? And why do you think he loves working with you? I know you’re going to have to maybe be really humble and be like, “I don’t know, why does he like me? I can’t understand.” Take a guess.

Alexi Lubomirski for Variety

MURPHY: With Chris, it’s just the work. He’s not interested in anything else other than the work and the filmmaking. And he’s incredibly focused, and it’s incredibly rigorous.

ROBBIE: When he called you and said, “Movie about Oppenheimer,” were you like, “Gotcha”? Or were you like, “Who’s that? I should go read a book.”

MURPHY: I knew the very basic Wikipedia level. I knew about the Trinity tests, and I knew about the Manhattan Project and then obviously what happened in ’45. But I didn’t know what happened afterwards or anything like that.

ROBBIE: So you read a lot to prep. What else did you do?

MURPHY: Walk around my basement talking to myself.

ROBBIE: Really? I prep like a psychopath as well. Did you have a thing that would get you into him?

MURPHY: Physically, there was loads of pictures of him, and he always stood with his hand on his hip. He was such a slight man, but he always stood with this very kind of jaunty angle. So I nicked that pretty early as a physical thing. And then Chris Nolan kept sending me pictures of David Bowie, like in the Thin White Duke era, with the big voluminous trousers.

And how about you? Such a difficult character. It’s this kind of 20th-century icon, but not a real person. How did you figure it out?

ROBBIE: It was so weird prepping Barbie as a character. All my usual tools didn’t apply for this character. I work with an acting coach, and I work with a dialect coach, and I work with a movement coach, and I read everything, and I watch all the things. I rely on animal work a lot. I was maybe 45 minutes into pretending to be a flamingo or whatever, and I was suddenly like, “It’s not working.”

I went to Greta, like, “Help me. I don’t know where to start with this character.” And she’s like, “OK, what are you scared of?” And I was like, “I don’t want her to seem dumb and ditzy, but she’s also not meant to know anything. She’s meant to be completely naive and ignorant.” And Greta found this episode on “This American Life,” where it was a woman who can’t introspect, who doesn’t have the voice in her head that’s constantly narrating life the way we all do. This woman’s got a Ph.D. and is extremely smart, but just doesn’t have that internal monologue.

MURPHY: Is she happy?

ROBBIE: Yeah, totally.

MURPHY: Is she happier, do you think?

ROBBIE: Oh God, I wondered about that. She kind of thinks about exactly what’s in front of her — a spotlight to what exactly is in front of her at the time.

MURPHY: Well, that’s perfect, right? We should talk about the costumes. So you’re clearly still not sick of pink then?

ROBBIE: No, I’m not done with pink yet. Yeah, the costumes were incredible. I mean, you just can’t have a “Barbie” movie without the color pink. And everyone really got on board with that. I’d make a “On Wednesdays, we wear pink” day. Do you know that reference from “Mean Girls”?

MURPHY: I had forgotten that reference.

ROBBIE: On Wednesdays, they wear pink. And so if you didn’t wear pink on set, you got a fine. And then I’d donate it to charity. It’s always the guys, I feel like, that are like, “Oh, finally I have permission to wear pink and get dressed up!” It would get crazier and crazier until Ryan would be like, “I think I need a mink.” It would just get insane.

In my opinion, there are two kinds of people in this world. There are the people who are obsessed with “Peaky Blinders,” and then there’s the people who haven’t seen “Peaky Blinders.” I obviously sit in the first category, so can we please talk about Tommy fucking Shelby for just one minute? I mean, that was years and years of your life.

MURPHY: Yeah, it’s like 10. That was also a 10-year adventure. We started shooting at the end of 2012.

ROBBIE: Is there going to be a spinoff movie?

MURPHY: I mean, I’m open to the idea. I’ve always thought that if there’s more story to tell …

ROBBIE: Please do it. Please! Obviously, I’ve now revealed that I am a big fan of yours, not just “Peaky Blinders.” I also love your sleep story on the Calm app. But because I’m a fan of yours, I have watched a lot of your things on YouTube, and it’s out there on the internet that you are not that aware of memes and things like that. First of all, is that true? And second of all, if that is true, were you even aware of the Barbenheimer phenomenon, or were you just blissfully unaware because you use a dial-up phone or something?

MURPHY: I have two teenage boys. I do know what a meme is. Now I know that there are memes about me not knowing what a meme is.

ROBBIE: It’s a great meme. It’s like the “Inception” of memes. A meme within a meme.

MURPHY: Genuinely at the time I did not know. But people forget that was a long time ago.

ROBBIE: I might not have known back then what a meme is. I’m not that tech-savvy.

MURPHY: Exactly. And I think children started that stuff, right? Now that it’s become this sort of meme that’s eating itself, I am aware. But it’s mostly because of people either sending it to me or showing me and saying, “Look, you gotta look at this.”

ROBBIE: You see any of the Barbenheimer fan art?

MURPHY: I mean, it was impossible to avoid any of that stuff.

ROBBIE: Weren’t there some great ones? People are so clever. People kept asking me, “So is each marketing department talking to each other?” And I was like, “No, this is the world doing this! This is not a part of the marketing campaign.”

MURPHY: And I think it happened because both movies were good. In fact, that summer, there was a huge diversity of stuff in the cinema, and I think it just connected in a way that you or I or the studios or anybody could never have predicted.

ROBBIE: You can’t force that or orchestrate that.

MURPHY: No, and it may never happen again.