Superman is a fictional character defined by his literally perfect, Adonis-like physique and most every actor who has played him over the years has had to commit to working out at least a little bit so they don’t look ridiculous in the Man of Steel dick-huggingly tight suit. A fact that resulted in Christopher Reeve having to train with Darth fucking Vader.
You see when Reeve first auditioned for the role of Superman everyone involved with production was split on whether or not he was a good fit with half the crew thinking he’d make a pretty good Superman and the other half, not so much. According to people familiar with the situation, the half of production who liked Reeve for the role hinged their reasoning on his piercing blue eyes and imposing 6ft 4 inch frame while the half didn’t agree because he was too skinny. A descriptor not many would use for wide-boy Superman.
The thing is, even the camp that felt Reeve was nowhere near wide enough to portray the Last Son of Krypton still thought he really fucking looked like him and were convinced to cast him on a solitary condition. He got swole.
Luckily for Reeve the film’s director, Richard Donner, just so happened to know Darth Vader, a character who knows a thing or two about lifting shit. Albeit, with the assistance of an indestructible robot hand and pseudo-telekinetic powers.
Specifically Donner knew the man who physically portrayed the Dark Lord of the Sith in the original trilogy, David Prowse, a bodybuilder and gym instructor with a chest 3 feet wide and a degree in being large and in charge. According to Prowse he immediately put Reeve to work, basically force-feeding him four protein-dense meals per day for several weeks straight whilst making him lift increasingly heavy things directly above his head.
Despite only having a few weeks to turn Reeve from a “beanpole” to a perfect specimen of humanity, Prowse was able to help the actor pack on 40 pounds of muscle before filming began. A feat we feel only a guy who could make a plastic suit of samurai armor and a cape made of carpet look intimidating could pull off.