It turns out Psylocke wasn't always supposed to be in "X-Men: Apocalypse" -- let alone one of Apocalypse's Four Horsemen -- but it was partially thanks to fan art that writer-producer Simon Kinberg gave Olivia Munn the major part in the film.
Speaking to Cinemablend, Kinberg revealed that Xavier was originally supposed to be the fourth Horseman after his capture in the middle of the film, not Psylocke: "The one person we didn't know was Psylocke, and the reason why is because originally in the script we sort of... I don't 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 that's the way we constructed the original draft of the script. There wasn't 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, 'He's not really a Horseman - he's not doing anything in the third act of the movie.'"
Kinberg noted that he thought about casting Munn as Psylocke after meeting with her for "Deadpool" -- for which she turned down the role of Wade's girlfriend, Vanessa -- and was swayed by fan art: "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."
Directed by Bryan Singer and starring James McAvoy, Michael Fassbender, Nicholas Hoult, Jennifer Lawrence, Oscar Isaac, Rose Byrne, Alexandra Shipp, Sophie Turner, Kodi Smit-McPhee, Evan Peters, Tye Sheridan and more, "X-Men: Apocalypse" hits theaters stateside on May 27.