Some 70 years ago, Superman co-creator Jerome Siegel sold the rights to the hero to Detective Comics for $130. Detective Comics is now DC Comics and is owned by Time Warner unit Warner Bros.
Superman has been the subject of much legal wrangling over the years, a brief summary of which can be found on Wikipedia. On Wednesday, a federal judge ruled that Siegel's heirs were entitled to share of the copyright, but left Time Warner's international rights intact. How this will effect the future of Superman remains to be seen, as there is still much more legal wrangling to come.
It gets more complicated. According to the New York Times, "A similar ruling in 2006 allowed the Siegels to recapture their rights in the Superboy character, without determining whether Superboy was, in fact, the basis for Warner Brothers's 'Smallville' television series. The decision was later challenged in a case that has yet to be resolved, said Mr. Toberoff, who represented the family in that action."
If you're interested in learning more about the legal issues involved in comic book cases, check out this story from The National Law Journal.