John Turitzin, general counsel for Marvel, said the comic book giant is the sole owner of the copyright to characters created in part by Kirby since the artist worked for Marvel on a "for hire" basis, the New York Daily News said Saturday.
Heirs of Kirby, who died in 1994, said in notices dispersed to various companies that Marvel's copyright on Kirby's works would belong to them as of 2014.
"The notices filed by the heirs are an attempt to rewrite the history of Kirby's relationship with Marvel," Turitzin said.
Among the popular Marvel superheroes with ties to Kirby are Spider-Man, the Fantastic Four and the X-Men.
No responses from lawyers for Kirby's heirs regarding Marvel's claims were reported.