Some interesting info about Saw Gerrera from an EW intervew with Whitaker;
Source
About his armor seen in the trailers;
“This is his armored suit for flight, but also for maintenance,” Whitaker told Entertainment Weekly. “He’s been through so many conflicts and many wars, so it’s also about [repairing] some of the many injuries he’s had. He wears it all the time.”
Whitaker on Saw’s relationship to Jyn;
“He’s really close to her, and they have a very powerful relationship,” Whitaker says. “He’s talking about how you maybe make compromises that may harm people, or may harm the situation, or people may question it, but if you’re doing it for the good, there’s a positive thing about that. But what does it make you become? And how do you change as a person?”
(It seem like they know each other from before the events of he film.)
The actor briefly touched on the interesting topic about his change in appearance in the trailers:
Some theorized that this was a alteration brought about during reshoots for the movie, but Whitaker says it’s a switch that happens within the story. Given the extra gray in his beard, maybe we’re seeing Saw at two different stages of his life.
“We made some decisions about how the character was progressing. They had a lot of opportunity to make tweaks and different things,” he says. “You’ll see both.”