Ben Mendelsohn has provided some additional information about his character Director Krennic and his relationship with Darth Vader.
The recent Star Wars novel Catalyst has given some fans a decent amount about the history of Krennic and his association with the Empire. He has been with the Empire for decades, serving as a Corps of Engineers officer in the army of the Republic during the Clone Wars. Now he is the director of the Special Weapons Division, specifically the Death Star project and fulfilling the Emperor's desire for a weapon that can destroy entire planets.
Mendelsohn spoke with Empire Magazine about how Krennic and Vader do not get along, stating that:
"It's fair to say Lord Vader and [Krennic] aren't friendly. Darth is very much about the Force. Krennic is not really down with the whole mystical thing.He is truly a man that has made his own way up the chain through his own abilities. His weapon, for instance, is a very old type of blaster, because he's an old warrior duded. He's been put in charge of making this thing happen. And it's gonna get done!"