All the cool kids know that Jack Kirby was the criminally unsung counterpart to the more visible Stan Lee. As an artist par-excellence at Marvel in the 1960s (and sporadically afterwards), he co-created most of The House of M's superhero pantheon: Hulk, Iron Man, Thor, The Fantastic Four (including Doctor Doom and The Silver Surfer),** Captain America**, the original X-Men...
Under the old-school 'work for hire' system however, writers and artists retained few to no rights to characters they created, and Kirby died in 1994 after several legal battles with Marvel that only ended in relatively unsatisfactory (for Kirby) compromises.
Now, with the cha-ching of Disney's $4bn Marvel buy-out still ringing in our ears, Kirby's heirs - his four children - have launched a new legal assault against Marvel. Specifically, they've issued 45 notices of termination of copyright, which if successful, would see Kirby's share (whatever that's deemed to be) in all his characters returned to his estate, as and when the current rights deals expire over the next decade or so.
That would obviously mean serious repercussions for Disney, Universal (who currently have movie distribution rights for Hulk), Sony (Spider-Man), and Fox (The X-Men and the FF), not to mention various merchandising licensees. Kirby's heirs would be entitled to a chunk of the profits of any Kirby-related Marvel media, plus, of course, having the option to sell their share on to the highest bidder.
By no coincidence at all, the Kirby estate's legal representation comes from the LA-based Toberoff and Associates, who recently scored some hits against Warners for Superman creator Jerry Siegel's estate. Those results are some indicator of just how complicated this could get. While Warners won some sort of victory early on in the proceedings, allowing them to keep Supes as long as a film was forthcoming in the not-too-distant future, the final result was that Warners and DC lost bits of the Man of Steel. The Siegels own Superman, Clark Kent, Lois Lane, The Daily Planet and the origin story (including Krypton and Jor-El), while Warners / DC retain Lex Luthor, Kryptonite, Jimmy Olson, and the fact that Superman can fly.
So we could potentially see Marvel having to sign over Professor X and Magneto, while keeping Wolverine, or losing Tony Stark but keeping Steve Ditko's red and gold Iron Man armour. We're trying not to think of the legal knots the projected multi-heroed Avengers movie might have to untie.
It's a moot point though, since Avengers should be safely in the can well before the Kirbys have the chance of throwing a spanner in the works (2017 at the earliest). Disney released a statement saying that the termination notices were "fully considered in the acquisition". If they're scared, they're not admitting it.