Wonder Woman 1984 dug deep into the DC Comics canon for Simon Stagg. The character is definitely a lesser known one, with no direct ties to Wonder Woman or any of her allies. That doesn't mean he's not interesting. For starters, though Stagg is a villain, he teeters on the line between good and evil, continually trying to better himself for the sake of his daughter, Sapphire Stagg.
First appearing in 1965 in The Brave and the Bold vol. 1 issue #57, Stagg is introduced as the founder and CEO of Stagg Industries who works in research and invention, alongside his daughter Sapphire and a man named Rex Mason, who are in love with each other. When Stagg sends Mason to Egypt to secure an artifact, the young man becomes exposed to the rays of a meteor trapped in a pyramid. Through this, Mason becomes the Elemental Man, also known as Metamorpho, and can now change his body into any element at will.
As Stagg works on a cure, he occasionally helps Mason and Sapphire use Metamorpho's power for good, but really, he wants Mason out of the way and away from his daughter. Stagg tries to keep them apart by any means, even if it harms Mason. Like Lord with his son Alistair (Lucian Perez), Stagg's only allegiance is to his daughter. Throughout his comic book storyline, Stagg goes back and forth between good and evil depending on how he feels about Mason and what he sees as best for his daughter.