Comics legend Stan Lee's former company, Stan Lee Media, has filed a massive lawsuit (which you can read at that link thanks to Deadline Hollywood) against the Walt Disney Corporation, alleging that Disney does not own any of the characters that Lee co-created and asking for “the maximum statutory damages allowable” as well as ownership of Lee-created characters from Marvel's character library.
Stan Lee is credited with co-creating Spider-Man, the X-Men and The Avengers, to name a few. He is currently not associated with Stan Lee Media.
"The Walt Disney Company has represented to the public that it, in fact, owns the copyright to these characters as well as to hundreds of other characters created by Stan Lee. Those representations made to the public by The Walt Disney Company are false,” claims the lawsuit filed in Colorado.
Stan Lee Media claims that Lee signed over the rights to all comic book characters he had created to them in October 1998. A month later, Lee reportedly signed a deal with Marvel reaffirming their ownership of characters that he co-created with them in what likely was an attempt to avoid a lawsuit like this.
"In November, 1998, Stan Lee signed a written agreement with Marvel Enterprises, Inc. in which he purportedly assigned to Marvel the rights to the Characters. However, Lee no longer owned those rights since they had been assigned to SLEI previously. Accordingly, the Marvel agreement actually assigned nothing,” alleges Stan Lee Media in the suit.
Stan Lee Media faces an uphill battle to win such a lawsuit; Lee did not individually create any characters for Marvel, always working with artists and therefore not really able to unilaterally assign copyright. That said, even creators whose contributions are not in dispute have historically had a hard time getting anything from Marvel and DC Comics for the characters created under comics's standard work-for-hire deals. Lee may have had a slightly different deal in place due to his editorial role during most of his time at Marvel but it seems unlikely that it would have been different enough to assign him unambiguous copyright.
The suit, should it actually move forward, could also get ugly, dragging some of the comic book industry's dirty laundry out into the public eye in a way it hasn't been before. Lee's detractors often say he claims too much credit for the creation of characters and the writing of scripts in the early days of Marvel's superhero universe. While Marvel typically doesn't acknowledge such controversy, it's not implausible that they could trot out a litany of comics historians to poke some holes in Lee's own credibility in order to disprove the legality of the document he signed with Stan Lee Media.