Superman was a fictional comic book character and superhero created in the 20th century on Earth. Superman was considered an American cultural icon and many books, television programs, and films were based on this character.
When Malcolm Reed and Trip Tucker were waiting for rescue in their disabled shuttlepod, Reed told Tucker that North Americans must read nothing but comic books. Tucker replied that Superman was "laced with metaphor. Subtext layered on subtext." (ENT: "Shuttlepod One")
Many Star Trek actors have appeared on TV incarnations of Superman, and a few have made appearances in the movies as well.
A Starfleet carry case was sold off on the It's A Wrap! sale and auction on eBay. As an inside gag, an inventory application on this case has the line "Don't tug on Superman's cape. Don't spit into the wind. Don't pull the mask off the old Lone Ranger and you don't mess around with Jim."