When you look at the huge success that Deadpool enjoyed both critically and commercially, it's hard to believe that the film was stuck in development hell for many years.
In fact, Ryan Reynolds was pretty open about the fact that this was the final attempt for to see the Merc With A Mouth on screen. Thankfully, it all came off and - as it stands - Deadpool is the fifth highest-grossing film of the year, earning $778 million off of a budget of $58 million. Not only that, a sequel's already underway.
However, back in 2014, it looked like there was very little that Fox could do to be persuaded of its potential. That was, of course, until two heavyweights stepped in to sing its praises. As co-writer Rhett Rheese explained, the cumulative effort of both David Fincher AND James Cameron reading the script at two different stages during development that helped out. "Each one of them was kind enough to go to 20th Century Fox and essentially throw in their good word just saying 'Hey, what are you guys doing with Deadpool? You should be making this!' David was a help before Jim and he was just kind of nudging along the way. And then Jim ultimately weighed in in a key decision node moment and got Fox to free up some money to try a PG-13 draft at the time - that was not Jim's idea, that was Fox's idea."
"But I think a project that is dormant often just suffers from neglect, and I think having those powerful people weigh in at certain times just lodged with Fox and I think it had a cumulative effect more than anything."
David Fincher's involvement has a lot to do with director Tim Miller. Before Miller's directorial debut with Deadpool, he worked as a VFX specialist and was responsible for the fantastic opening title credits for the US remake of The Girl With The Dragon Tattoo. James Cameron, however, has been around Fox for quite a while and clearly saw the potential for Deadpool.
It does say a lot about Fox's reluctance to see Deadpool made that it two of the most well-known directors to step in to talk up the film in order for it to be made. Thankfully, the gamble paid off for everyone.