Image caption Writer Jerry Siegel and artist Joe Shuster created the comic book superhero in 1932

Warner Bros have won an important legal victory over the heirs of one of the creators of Superman, giving it total commercial control of the superhero.

An appeals panel unanimously ruled that Jerome Siegel's heirs must abide by a 2001 letter accepting Warner's offer for their 50% share of Superman.

Though the five-page letter was never formalised into a contract, the appeals court said it was still binding.

The latest Superman film, Man of Steel, is due to be released this summer.

In his ruling, Judge Stephen Reinhardt, of the 9th US Circuit of Appeals, wrote both parties "had resolved the last outstanding point in the deal during a conversation on Oct 15, 2001".

He added the letter "accurately reflected the material terms they had orally agreed to on that day,"

The ruling undoes a 2008 court decision ordering Warner Bros. to share an undetermined amount of money earned since 1999 with the heirs, and to give the family control of key components of the Superman story, including his costume.

We are extremely pleased that Superman's adventures can continue to be enjoyed... for generations to come Warner Bros statement

Superman's co-creators, Joe Shuster and Jerry Siegel, battled for higher compensation for the comic book creation throughout their lives.

"The court's decision paves the way for the Siegel finally to receive the compensation they negotiated for and which DC has been prepared to pay for over a decade," said a statement from Warner Bros, on behalf of its DC Comics division.

"We are extremely pleased that Superman's adventures can continue to be enjoyed across all media platforms worldwide for generations to come."

Second case

While the Siegel family have yet to issue any comment, lawyer Marc Toberoff - who also acts for the heirs of co-creator Joe Shuster, has indicated that the Shuster heirs will appeal a different court decision from October 2012, which awarded Warner Bros all rights to the Superman character.

In 2010, DC Comics sued the brother and sister of Shuster, the artist responsible for the superhero, on the basis that they relinquished their ability to reclaim the copyrights in exchange for annual pension payments from DC Comics.

US District Judge Otis Wright ruled that Shuster's sister's decision to accept higher annual payments created a new agreement which cancelled any previous contract, adding the families of both creators have been paid in excess of $4m (£2.5m) since 1978, plus undefined bonuses and medical benefits.

Superman has generated more than $500m (£310m) for Warner Bros with five films at the US box office and billions of dollars more from television, toys and games, and comic books spanning 74 years.

British actor Henry Cavill takes over the role of Superman in the latest big screen instalment, with Oscar nominee Amy Adams as Lois Lane. It is expected to hit cinemas across the world on 14 June.