Who is Gregor from The Haunting of Alaizabel Cray and what is their importance?

Gregor is a self-admitted coward, a deserter from the Russian armed forces. He is an airship pilot at Finsbury Park. He pilots an airship to the Old Quarter so that Thaniel, Cathaline, Alaizabel, Devil-boy Jack, and Carver can try to defeat the Fraternity. Fear overtakes Gregor while the airship is tethered to a cathedral, and he drops bombs to break the ropes and fly away.