Superman was created by writer Jerry Siegel and artist Joe Shuster in 1933. They sold the copyright to Superman to Detective Comics (which became DC Comics) back in 1938 for $130 and other considerations.
In 1978, copyright law was changed to allow copyright owners to revert their copyrights back after 35 years. Siegel and Shuster’s families traveled a long legal road in an attempt to do just that. But that road just ended last week, when the Supreme Court declined to hear their appeal.
This is a complex and fascinating story.