Lex Luthor: Lenny, I've always considered you the Dutch Elm disease in my family tree.
Lex Luthor: He gets his energy from the sun. Without it, he's like you at night - useless.
Lex Luthor: Destroy Superman!
Nuclear Man: First, I have fun.
Lex Luthor: You know what I can do with a single strand of Superman's hair?
Lenny: You can make a toupee that flies.
Superman: You'd risk world wide nuclear war for your own personal financial gain.
Lex Luthor: Nobody wants war. I just want to keep the threat alive.
Lex Luthor: Lenny, let's try and keep your IQ a family secret.
Answer: There appears to be multiple reasons. They had creative differences, ultimately resulting in a poorly received movie. Kidder said Reeves, who co-wrote the story, had an inflated ego and clashed with Furie.
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Moreover, Mark Pillow, who played Nuclear Man, claimed that working with Reeve was quite intense.