James Cameron, George Lucas, Sylvester Stallone, and other directors who took a really longtime between movies.

After much talk, delay, and hype, James Cameron's Avatar is scheduled for worldwide release on Friday. For Cameron, it's been 12 years since his previous feature—the box-office phenomenon Titanic —made him king of the film world. Twelve years is a long layoff between features, especially for a director at his Oscar-winning peak. While he was away, George W. Bush came and went, Titanic's barely drinking-age heartthrobs Leonardo Di Caprio and Kate Winslet matured into their mid-30s, and Bill Paxton fell several letters beneath the A-list. What was Cameron up to?

He coasted on Titanic'ssuccess for a while, making TV and IMAX documentaries about various sunken ships and lending his name to some dubious-sounding, ancient-safe-cracking blarney, and he shook a few more coins from the Terminator franchise. In 2006, he scripted and started working on the technically intricate Avatar. But Cameron's layoff isn't the longest of all time; cinema has a rich tradition of drawn-out productions and slowpoke directors. What makes a renowned filmmaker go 10, 15, even 20 years between features?

The reasons are numerous, revealing, and occasionally hard to believe. Yet viewed together, patterns emerge. Ambition is frequently part of the equation, sometimes hubris. Budget problems and legal snags are common. Addiction, affliction, and madness sadly often play a role, as do political persecution and exile. Cameron's Avatar is nothing if not ambitious, but he should be glad he didn't have to flee from Fascists (as Carl Theodor Dreyer did) or direct without the ability to speak (Michelangelo Antonioni).

Our list isn't comprehensive, but aims to be representative of what caused some of the world's most celebrated filmmakers to have yawning gaps on their résumés. Often the story of what happened in between films is grander, and far stranger, than what eventually got made.

Click here to read a video slide show on long-gestating movies.

Become a fan of Slate on Facebook. Follow us on Twitter.