Answer: Predator

After the release of Rocky IV, a joke began circulating Hollywood: because Rocky had beaten every worthwhile Earthly opponent, he was going to have to fight an alien if there were to be a Rocky V. While that might not be the funniest joke to ever make the rounds, it got screenwriters Jim and John Thomas thinking. What if Rocky (or another over-the-top super hero like Rocky) faced off against aliens?

They set to work and cranked out the screenplay in a weekend (because they’d heard that’s how Rocky had been written).  The screenplay was picked up by 20th Century Fox, and then in turn given to producer Joel Silver. Silver was fresh off his work with the movie Commando and saw enormous potential in the script and pushed for it to be transformed from a Sci-Fi pulp-style film into a big-budget action film. Silver pitched the leading role to Arnold Schwarzenegger, who not only accepted the role but helped to shape the direction the movie was headed, and one of the most iconic action movies of the 1980s started production all thanks to a Hollywood joke.