With the first reviews of X-Men: Apocalypse hitting the web (to a collective meh, rather unfortunately), Simon Kinberg has been talking to CinemaBlend about the writing process of the sequel, and specifically how they chose which characters would make up Apocalypse's horsemen.
Kinberg says that originally there were only to be three horsemen, and that an early draft of the script considered Professor X to be the fourth after he was kidnapped by the villain. Ultimately that plan was passed on, and Psylocke was added last minute to the mix:
"The one person we didnt know was Psylocke, and the reason why is because originally in the script we sort of I dont know why we made this decision, but we knew that Professor X was abducted in the middle of the movie, and we thought that almost counted as a fourth Horseman. And so thats the way we constructed the original draft of the script. There wasnt going to be a fourth one. The surprise was that Xavier was the fourth Horseman. And then when we were working on the script, Bryan and I at one particular point pretty late in the process said, Hes not really a Horseman hes not doing anything in the third act of the movie."
In terms of choosing who would make the cut, Kinberg said he and Bryan Singer consulted a list of all of the Horsemen Apocalypse has used in the comics (thanks Wikipedia), and settled on Psylocke as the answer. It presumably helped that fans had called for her inclusion in X-Men movies almost since the series kicked off.
Kinberg also revealed that he had just met Olivia Munn for Deadpool, and had her fresh in his memory when they were considering Psylocke to the film:
We started talking about who that would be, and just literally looked at the list of different Horsemen over the history of the comics, and Psylocke was the one we thought was the most intriguing. And, ironically, or as fate would have it, I had just met with Olivia Munn about Deadpool - like a week or two before. And Bryan and I were up in Montreal, and I said, You know, Olivia Munn could be an interesting Psylocke, so we went on the internet and Googled her images. And one of the first things that popped up was a piece of fan art of Olivia as Psylocke."
So there you have it: proof that film-makers do look at the fan art you make when deciding who to cast. So never ever stop.
Perhaps this late addition accounts for why some reviewers have said Psylocke is painfully under-used. Whatever the case, let's hope she gets further chance to shine in future X-Men movies.