Darth Vader Played a Crucial Role in Helping Christopher Reeve Become Superman – The Hollywood Reporter

Calling the actor a "skinny little kid" when they met for his audition, Richard Donner made Reeve promise he would be able to bulk up for the role.

Spencer Wilding - News - IMDb

Superman' producer Ilya Salkind reveals secrets from the set: Christopher Reeve had to gain 40 lbs. of muscle

Superman: The Movie at 40; How it Changed Our View of Super Heroes

How Darth Vader Helped Christopher Reeve in his Superman Role

Why was Christopher Reeve's depiction of Superman so compelling? - Quora

Darth Vader Actor David Prowse Tried To Land The Lead Role in Richard Donner's SUPERMAN — GeekTyrant

Superman A Movie Celebration - Future of the Force

Christopher Reeve: Remembering the 'Superman' Actor's Career

David Pruss, the actor who embodied Darth Vader, the villain of Star Wars - Free Press

Star Wars Actor David Prowse, the Original Darth Vader, Dies at 85