Does Gatehouse represent the Angel of death/the devil? (spoliers)
His name is Gatehouse -- suggesting you pass him to go somewhere -- like Charon the ferryman who ferried the dead to the underworld
He seems to be indestructible -- he has supernatural skills and strength and has the heart of a 20 year old (he does not age).
He wants control -- like Lucifer before he was cast out of Heaven
He has no conscience or scruples and at the end he tries to tempt Jonah (Gabriel)over to the dark side, asking, "why do you do this...so you can stand in the light..."
just some thoughts i had