LOS ANGELES (Reuters) – British actor Christian Bale forced a rewrite of upcoming action movie "Terminator Salvation," because his star had grown too big for the small role of John Connor he chose, the filmmakers said on Friday.

Director McG, whose real name is Joseph McGinty Nichol, said he had the disconcerting experience of going to England to convince Bale to play central character Marcus Wright in the man vs. machines film, only to have Bale tell the director he wanted to play Connor instead.

McG told reporters that the script was a "moving target" that became a filmmaking challenge, and that he worked day and night with Bale, who starred last year in box office smash "The Dark Knight," talking about how to work Connor into the movie.

Connor is an iconic character in the film franchise that began in 1984 with "The Terminator," but his role was originally small in the series' fourth movie, "Terminator Salvation," which debuts in theaters on May 21.

"A lot of the work was integrating (Connor) into scenes ... and having that feel integral and sensible, as opposed to grafted on just because there was a star in the part," John Brancato, a screenwriter on the film, told reporters.

He said originally the main character was Marcus Wright, an executed death row inmate who donates his body to science, and re-emerges alive after machines have taken over the world by unleashing a nuclear holocaust on mankind. In the movie, Connor and Wright become equally important characters.

Wright is played by Australian actor Sam Worthington.

Bale said that he asked to be consulted about who would play Worthington opposite him.

"There's a benefit of currently a lot of people in the States not being familiar with him, and so you can really enjoy that performance that much more," Bale said. "He's got so many movies that are going to be coming out, because many other people have realized that he's bloody good."

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