Case closed, as far as Marvel’s lawyers were concerned.

The Kirbys fired back on March 9, filing a lawsuit with the Federal District Court in Los Angeles that argues the opposite. From 1958 to 1963, the period of Mr. Kirby’s prolific career that is under scrutiny, “Kirby worked solely on a freelance basis out of his own home, with his own instruments and materials, and thereby bore the financial risk of creating his copyrighted materials,” according to the lawsuit.

Mr. Toberoff is poised to argue that Mr. Kirby — and, by extension, others like him — were selling their work on a freelance basis, rather than serving as hired hands.

THE Kirby case is virtually certain to reopen the much-chewed-over history of Marvel to an examination even more intense than it has received from comic book fans. Many fans believe that Marvel and Stan Lee — who once wore varied professional hats, including editor in chief and publisher at Marvel — assigned too little credit to the contribution of an artist they like to call “King Kirby.” Mr. Kirby has drawn lavish praise from such luminaries as the novelist Michael Chabon, who has described him as “the Shakespeare or Cervantes of comic books.”

Mark Evanier, who worked as an assistant to Mr. Kirby and wrote the book “Kirby: King of Comics,” said he expected to be called as a witness in the case and declined to comment. Mr. Evanier testified in support of the Jerome Siegel heirs in their suit against Warner.

Mr. Lee, now 87, will surely have his own version of past events and is almost certain to become a witness in the case if it goes to court. Mr. Lee — who notably fought and won a profit-participation lawsuit with Marvel a decade ago — declined to be interviewed for this article.

If Mr. Lee is called to testify about Mr. Kirby, his testimony could be complicated by an expanded business relationship with Disney. On Dec. 31, Disney announced that it had paid $2.5 million to increase an already existing stake in POW Entertainment (for Purveyors of Wonder), a company in which Mr. Lee is now a principal and the chief creative officer. POW develops new characters and stories for use in comic books, films, digital media and elsewhere. At the time, Disney said the investment was meant to obtain Mr. Lee’s help in mining the Marvel library.

If Mr. Toberoff has his way, the picture painted in court will be one of chaos. He says that during Marvel’s early days — when Mr. Kirby was creating his superheroes — the company was a shoestring operation that was barely afloat.

“There was no bullpen; there was a one-man office,” he said, contending that an industrywide decency code put so much pressure on Marvel that few at the company were worrying about contractual niceties with artists like Mr. Kirby that would have tidied up all of the legal issues surrounding work arrangements. “It’s easy to imagine that nobody at the time was thinking about work for hire.”