In a video message posted online this week shortly after Walt Disney announced its $4bn purchase of Lucasfilm, Bob Iger, Disney's chief executive, told viewers what the media group was getting for its money.

"Seventeen thousand characters that inhabit several thousand planets spanning 20,000 years," he said. Disney had not just bought the company behind Star Wars, one of the most lucrative film series ever released: it had also acquired a virtual "universe" of intellectual property, he said.