Captain Cushing is an officer of the Imperial Navy and the Captain of the Black Prince, though in practice he's usually forced to defer to Inquisitor Sutherland and the Order of Inquisitors, to whom the ship was assigned. He's sixties-ish, belying a history in probably the Navy of the Republic during the Clone Wars, with really cool sideburns from either the 1870s or 1970s.
Plot hooks
Captain Cushing hates Inquisitor Sutherland, and grows increasingly suspicious of his motives and questions the orders he gives that seem to conflict with the overarching goals of the Empire (though Palpatine gives up Death Star plans to set traps all the time, so, you know… it happens).
Behind the scenes
The character is a little bit inspired by Domhnall Gleeson's sequel trilogy character, General Hux. While nobody in those shit movies really had a good arc, Hux was done especially dirty and probably deserves a little bit of redemption. We're going to borrow his strict military mindset and distaste for his angsty Dark Side contemporary, but throw away the lazy spy reveal and unceremonious death.
Captain Cushing is named for both American naval officer William B. Cushing and English screen actor Peter Cushing, who obviously played Grand Moff Tarkin in Episode IV.