December marks the 40th anniversary of the “Superman” movie, which opened Dec. 15, 1978, and influenced generations of action films. In recent years, many people were distressed that Claire Foy was paid less than Matt Smith for Netflix’s “The Crown,” but pay gaps are not always about sexism. Blame the star system. Back on June 30, 1976,Variety reported that Marlon Brando agreed to play the title character’s father in “Superman” for a salary that was “unprecedented.” It was eventually revealed that the actor was paid $3.7 million and an amazing 11.75% backend to play Jor-El, for 13 days work and less than 20 minutes onscreen. In comparison, Christopher Reeve earned $250,000 in the title role, dominating most of the 143-minute running time.

Brando was at the height of his power, after “The Godfather” and “Last Tango in Paris.” In 1976, exec producers Ilya Salkind & Alexander Salkind and producer Pierre Spengler needed a star to get financing. “Star Wars” hadn’t opened. After the low-tech “Adventures of Superman” TV series of the 1950s and the camp “Batman” series in the 1960s, comic-book superheroes were the butt of jokes. Even in the 1970s, Brando’s payday seemed excessive, but in fact it was an investment. If he hadn’t signed on, it’s possible the film would never have been made. Brando was the crucial first step, and Gene Hackman as Lex Luthor cinched it.

The producers couldn’t film in Italy due to Brando’s legal troubles there, centering on the then-scandalous “Last Tango.” The Salkinds planned to move production to England, but director Guy Hamilton couldn’t film there because of his status as a tax exile in the nation. So Richard Donner took over.

It was a successful choice, but not a happy one. Donner basically filmed the first and second “Superman” films simultaneously. But he was fired and Richard Lester took over. The first film was credited to Donner, the second to Lester.

In 2006, the DVD release of “Superman II: The Richard Donner Cut” included more Brando scenes. At public events tied to the DVD release, 30 years later, it was clear that bad feelings persisted. But Donner, the producers and the screenwriters set the template for subsequent movies about characters from D.C. Comics and Marvel Comics for decades to come. Tim Burton’s 1989 “Batman” grossed $411 million worldwide, more than 10 times its budget, and the modern superhero mania was born.

And, as a further reminder that the 1970s were a foreign country: Bruce Jenner was considered for the title role in the first “Superman,” after his 1976 Olympics decathlon triumph established him as an all-American hero.