He’s a superhero to rights holders — but Kryptonite to studios.

Last week, attorney Marc Toberoff won a potentially costly “Superman” victory against Warner Bros. for co-creator Jerome Siegel’s heirs. The federal ruling, which gives the heirs a stake in rights sold 71 years ago, could put a serious crimp on future plans for one of the studio’s most enduring — and lucrative — franchises, especially if co-creator Joe Shuster’s heirs follow suit in five years, when they are eligible to do so.

As it is, the studio has at least two Superman projects in development — a follow-up to Bryan Singer’s “Superman Returns” and “Justice League” — and it may end up paying tens of millions from the domestic haul of “Superman Returns” to Siegel’s heirs under the ruling, which applies to domestic monies for Superman projects since 1999.

The case is Toberoff’s latest — and potentially most damaging — claim against the studio. The dedicated copyright crusader has pursued claims involving “Wild Wild West,” “Dukes of Hazzard,” “Smallville” and the upcoming “Get Smart.”

He has gone after other studios, including Sony, but his most high-profile cases — and victories — have involved Warners. The studio paid “Moonrunners” producer Robert B. Clark a $17.5 million settlement in a case about similarities between that 1974 movie and the bigscreen “The Dukes of Hazzard.” And a federal judge ruled earlier in the Siegels’ favor over “Smallville,” although that was challenged and the case still being resolved.

The studio declined to comment on the latest ruling in favor of their legal nemesis, issuing only a statement noting that, “substantial issues relating to the accounting of profits were ruled in our favor.”

Among these issues: international profits, trademark-related revs and profits stemming from Superman fare produced before 1999, when Siegel’s heirs terminated the earlier copyright arrangement under a 1976 law.

To the Siegels, Toberoff’s legal maneuvers are nothing short of heroic. The family had been destitute for years after Siegel sold rights to his Man of Steel to Detective Comics for $130. DC Comics had started to pony up more monies after Warners made successful movies based on the character, but Siegel had long wished to redress the fact he had gotten so little from his creation; he died in 1996.

Toberoff has set up a production company, Intellectual Properties Worldwide, to develop films around these and other titles. And he has built up a sideline business producing bigscreen adaptations of the projects whose copyright claims he pursues. He has a producing credit on “Fantasy Island,” a Sony project for Eddie Murphy, as well as “Sanford and Son.”