Executive producer Ilya Salkind would never have guessed that his childhood comic book hero would ultimately define his career.

He was 31 years old when he was given the chance to bring "Superman" to the big screen for the first time — and that was the 1978 hit that would transform Christopher Reeve and Margot Kidder into box office sensations.

A true superhero fan, 71-year-old Salkind recently attended the Hollywood Museum in support of its current exhibition “Superhero Legends,” which honors the Man of Steel and other iconic figures from cinema and comic book history.

He also recently spoke with Fox News about all things “Superman” and didn't hesitate to share his secrets from the set.

'Zorro' inspired Salkind to produce ‘Superman’

“I was walking in Paris and there was a movie about Zorro,” he explained. “And that gave me the idea to do a comic-book movie. I had read Superman as a kid, but somehow that idea just came out.”

Actress Margot Kidder shown in a scene from the 1978 movie "Superman" with Christopher Reeve. (Warner Bros.)

Ilya Salkind pushed for a ‘Superman’ movie

Salkind had wrapped up working behind-the-scenes in 1974’s “The Four Musketeers” when he was brainstorming for ideas on a new film to work on alongside his father, film producer Alexander Salkind, over dinner. “I said out of the blue, ‘Why don’t we do Superman?’" Salkind recalled. “My father didn’t know at all what Superman was. I said, ‘He flies, he has powers.’ And he said, ‘Oh, that sounds interesting. Let me talk to my backers about the idea.'" The following day, Salkind’s father gave him the green light to make the film happen.

Sylvester Stallone wanted to become Clark Kent

While Salkind was impressed by Stallone’s performance in 1976’s “Rocky” during a screening before the film was premiered to the public, he just didn’t think the actor would work as the Man of Steel. “He wanted to do it,” said Salkind. “He absolutely wanted to do it. But he just wasn’t right for the part. ‘Hey yo, Louis!’ It wasn’t Superman.”

Sylvester Stallone and Brigitte Nielsen attend the 15th Annual American Film Institute (AFI) Lifetime Achievement Award Salute to Barbara Stanwyck on April 9, 1987 at the Beverly Hilton Hotel in Beverly Hills, California. (Getty)

Many stars were considered for Superman

Salkind revealed that DC Comics, which owns the rights to Superman and approved a film adaptation, also had a wish list of actors they approved for the leading role. “They had people like Al Pacino and Dustin Hoffman who were approved, but they were totally wrong for the role,” said Salkind. “Stallone was approved too by the way. Robert Redford, Clint Eastwood — they both turned it down. We also tested Bruce Jenner, but he was just not a good actor. He didn’t have any acting experience. So we didn’t take him."

Christopher Reeve was an unknown

While Reeve is hailed today as a Hollywood legend, he was a relatively unknown actor looking for his first big break when he auditioned for the role. At this point, Salkind was looking for a newcomer and had even considered the dentist of his first wife, “Fantasy Island” star Skye Aubrey, who ultimately wasn’t a right fit. Reeve, who was a towering 6’4”, seemed promising for the superhero role, except he still had plenty of work to do. “He read the part of Superman and Clark Kent and it was fantastic,” said Salkind. “But he was very, very skinny. Too skinny. So we went on to test many others.”

Christopher Reeve posing for shot; circa 1970. (Getty)

Reeve made a major transformation

After numerous actors tried out for the role of Superman, Salkind still didn’t have his leading man. However, Reeve’s performance left a lasting impression on him, one he couldn’t deny. “We couldn’t find anybody,” said Salkind. “So I said, ‘Look, let’s have Reeve work out.’ So we flew him back to London and he did the test in costume. He was fantastic again. So we said, ‘Alright, but can you bulk up?’ He said yes and started to work out incredibly. English bodybuilder David Prowse, who physically portrayed Darth Vader in 1977’s “Star Wars,” was chosen to train Reeve, who began eating up to six meals a day. “He gained about 40 pounds of muscle,” said Salkind. “He totally changed.”

‘Superman’ had a completely different director

“We originally had Guy Hamilton, who did ‘Goldfinger,’” said Salkind. “He was in Rome, where we were filming at first, but he couldn’t stay because he had a tax problem. So he had to leave every week to Paris. After a few weeks, he was just too tired and couldn’t take it anymore. So then we took [director] Richard Donner.”

American actor Marlon Brando with British actress Susannah York. — Getty

Marlon Brando was difficult — at first

Salkind was overjoyed when Brando, who was at the height of his career with 1972’s “The Godfather” and “Last Tango in Paris,” agreed to take on the role of Jor-El, Superman’s biological father. However, he didn’t make things easy for the film’s producers at first. “When we met him in Los Angeles to discuss his costume, he went on completely different topics about [Native Americans] and all kinds of things,” explained Salkind. “Then at that point, Brando said he should play Jor-El as a green suitcase. I almost had a heart attack.

"I thought that was it, this is the end, it’s over. This man is crazy and he’s going to destroy the movie. He went on and on about this green suitcase. Then it became the green bagel. And finally, he said, ‘What do you think?’ He was really testing Donner to see if he would go along with it. But of course, Donner said no. Donner said, ‘Everyone knows Marlon Brando and that’s the person everyone wants to see.’ Brandon said, ‘You may be right.’ And from there he was absolutely perfect.”

Leslie Ann Warren and Stockard Channing tried out for Lois Lane

When it came to finding an actress who could embody brunette beauty and scrappy reporter Lois Lane, Salkind said Leslie Ann Warren was originally considered for the part, and that she was tested at the same time as Stockard Channing. While Warren seemed like a possibility, Channing was not. “We thought Channing looked too much like the mother of Superman,” said Salkind. However, a clumsy actress named Margot Kidder auditioned for the role and Salkind was quickly moved. “She was absolutely fantastic,” said Salkind. “She created her own Lois Lane. There’s no question that it would have been very hard to get a better Lois Lane.”

Margot Kidder (Getty)

Making Superman fly was a whole new challenge

Salkind and his crew were determined to make Reeve’s flying scenes, which were crucial to the film’s success, as lifelike as possible. Reeve and Kidder were supported by a harness, but it delivered a whole new set of problems. “Reeve was very disciplined,” said Salkind. “He was on it for hours and hours. Kidder hated it. She didn’t like to be in the harness at all. She thought it was uncomfortable and just wasn’t into the height situation.” Salkind added that back then, computer-generated imagery (CGI) wasn’t available, so they also relied on wires and trampolines. The cast even had to leave Rome and film in London, where Salkind found “the best technicians” to help him make Superman fly. “Funny enough, the movie got an Oscar for special effects,” he said.

Reeve remained grateful

Salkind said Reeve was not only completely dedicated to the role of Superman, but he was willing to do whatever it took to make the film a success. “He was always on time,” he said. “He would do retakes as many times as he had to. When the film was announced, there was a lot of press. But he remained very confident about his performance. He did whatever it took to promote the film. He was very nice to the press and never refused an interview."

Christopher Reeve in "Superman." (Getty)

The cast stayed in touch

Salkind said he stayed in touch with the cast even after “Superman” premiered in 1978. “I last saw Margot Kidder in a few conventions a couple of years ago,” he said. “She was very sweet. Brando and I actually did another film together, [1992’s] "Christopher Columbus: The Discovery." Reeve and I were very, very close. Usually, producers and actors have a working relationship, but it’s pretty rare for it to stay friendly. But he and I were very good friends. I was devastated when he [later] had his accident.”

Salkind isn’t impressed by today’s Superman

British actor Henry Cavill stirred headlines for recently becoming the new Superman, but Salkind just isn’t impressed by his rendition. “‘... That [movie] was pretty average,” he said. “I thought it was wrong because it was trying to be too much like Batman. He killed and did things Superman does not do. Superman never kills.”