An early version of Star Trek: The Motion Picture (1979) would have culminated in Captain Kirk fighting an alien disguised as Jesus, according to a new unauthorised oral history of the series.

The Fifty Year Mission by Edward Gross and Mark A Altman revealed that the show’s creator, Gene Roddenberry, worked on a number of concepts, including a time-travel adventure in which the crew attempts to stop the Kennedy assassination. But the most offbeat idea featured a shapeshifting alien that could manifest as biblical figures.

“In the climactic scene, Kirk had a fistfight with an alien who had assumed the image of Jesus Christ,” Star Trek author and screenwriter Michael Jan Friedman said. “So Kirk was slugging it out on the bridge. With Jesus.”

Friedman was hired to turn the unmade screenplay into a novel but struggled with disjointed material that included “some mildly erotic, midlife-crisis stuff”.

“Gene was – and still is – one of my heroes, for God’s sake,” he said. “As he had already left the land of the living, this was a unique opportunity to collaborate with him. But when I read the material, I was dismayed … [It couldn’t] possibly have been his best work.”

The release of the book coincides with the latest film in the franchise, Star Trek Beyond, the third in the rebooted saga starring Chris Pine and Zachary Quinto. Next year, a new Star Trek TV series by Bryan Fuller, known for Hannibal and Pushing Daisies, will debut.