Music mogul Simon Fuller has launched legal action against TV host Simon Cowell, claiming his X Factor ITV1 show copies his Pop Idol format.
Cowell (centre) with Louis Walsh and Sharon Osbourne on X Factor
Fuller's company 19 TV, which created Pop Idol and American Idol, is taking action against producer FremantleMedia, Cowell and his firms Simco and Syco.
"19 TV will be pressing for a speedy trial to resolve the matters as swiftly as is possible," a 19 spokesman said.
FremantleMedia denied the claim, while Cowell branded it "utterly ridiculous".
19 is claiming breach of contract and breach of copyright.
Cowell became a household name after appearing as an outspoken judge on ITV talent show Pop Idol, which first aired in 2001.
The show, which helped create pop stars Will Young, Gareth Gates and Michelle McManus, attracted 12 million viewers for the final of its second series in December 2003.
He was also a judge in the show's US equivalent, American Idol, which won more than 31 million viewers during its final in May.
He has now set up a production company, Syco, and appears as a judge in its first show - The X Factor.
Simon Fuller was behind the success of the Spice Girls and S Club 7
A talent show in which wannabes face Cowell and fellow judges Sharon Osbourne and Louis Walsh, The X Factor's first episode was broadcast on Saturday.
As well as claiming copyright infringement, 19 TV is suing for breach of contract because it claims a number of X Factor's production team also worked on Pop Idol and signed contracts that restricted them from working on rival shows.
But Cowell branded the claim "totally and utterly ridiculous".
Spokesman Max Clifford told BBC News Online: "Does this mean that Granada could sue the BBC for creating EastEnders because it made Coronation Street first?
"Look at New Faces, Opportunity Knocks, there have always been television talent programmes.
"Indeed, Popstars' producers tried to sue Pop Idol and that didn't get anywhere."
FremantleMedia - whose Talkback Thames subsidiary produces X Factor - said in a statement: "We deny the allegations made in the writ and in the press. We will defend any action vigorously and we hope to resolve the matter amicably."
"The X Factor is a different format to Pop Idol," it added.
Simon Fuller, who runs management company 19, was the man behind enormously successful pop acts such as the Spice Girls and S Club 7 before creating Pop Idol.
Last year, he was named the most influential person in the UK music business by industry magazine Music Week.
He also became the first British music manager since The Beatles' Brian Epstein to hold the top three positions in the US chart, with singles by artists from American Idol.