In Kojima Station episode 6, the studio’s official podcast, Kojima Productions staff members gave some insight into the casting process for Metal Gear Solid V in response to a question sent in by a fan about why they cast Troy Baker to play Ocelot (who was previously voiced by Patric Zimmerman and Josh Keaton). Assistant producer Sean Eyestone responded to this question.
It really goes based on the role. We don’t specifically, generally don’t look and say: we want this actor in particular. It’s more, we have an audition process. […] We had a bunch of people come in and audition for all the various roles. What we were looking for was a little bit of an older Ocelot. A little older than what he was in MGS3, but not quite as old as he was in MGS1. So someone who could fill that gap in between.
We also needed somebody who could do a lot of good facial capture as well because that is something that has been added this time: not just voice but also facial. […] And also someone who kind of had a similar face [to Ocelot]. That came from our animators, that we want to make sure that person who does the facial capture actually has a face that’s compatible to the characters.
Christopher Johns added:
It was actually very hard to find the right actors for everybody, because it had to be compatible facially and have a great performance, and good acting.
There was an extra layer added onto that – usually we just listen to the audio when we make our decisions […], this time we also had pictures sent in and video.
These were then sent to the animators to see if they could use the actor.
Troy had the right look, he had the right voice, and he of course has the acting skills. So that’s how we arrived at Troy, and everyone else in the cast as well. And we’re fortunate to have a really great cast, we’re very happy with that.
Source: Kojima Station Episode 6