Which characters are involved? Many of the superheroes central to the Marvel Cinematic Universe, including Iron Man, Spider-Man, Dr. Strange, Captain Marvel, Ant-Man, Hawkeye, Black Widow, Falcon, and Thor.
And which creators are we talking about? Those who served termination notices are the estates of illustrators Steve Ditko and Don Heck, the heirs of writers Don Rico and Gene Colan, and the 89-year-old Larry Lieber, comics writer and artist (and brother of Marvel legend Stan Lee).
What is the dispute, exactly? It hinges on one question: whether these artists created the superheroes as works made for hire — that is, under employment by Marvel — or as independent works made on a freelance basis, then sold to Marvel. If it’s the former, as Disney argues, then the termination notices are invalid and Marvel holds onto the copyrights. If it’s the latter, ownership of the characters must partially return to the creators or their heirs.
And what would that mean? That Disney would have to send the estates a portion of (but not all) the profits of any new works that use these characters. Marvel films are lucrative, to put it mildly, so a lot of money is at stake. Note: the law here only applies to the U.S., so Disney will in any case get to continue controlling the IP overseas.
Where does animation come into this? Marvel has used these characters in a range of animated productions, most recently the Disney+ series What If…? And more is coming: the studio has recently signaled its growing commitment to animation.
Is there precedent for this kind of case? Yes. Disney zealously guards its IP. From 2009 to 2013, Marvel fought the heirs of comics legend Jack Kirby over the ownership of characters like Thor and the X-Men; two courts sided with Marvel before the dispute ended in a settlement. In general, Disney has lobbied intensively for the legislative extension of copyright terms, with much success.