Who is Policeman Fox from The Third Policeman and what is their importance?

Policeman Fox is the third policeman. He is supposed to have been driven insane by looking at the patent color that MacCruiskeen invented, which is on a card inside a box in MacCruiskeen's room. Fox warns the other policemen that a group of one-legged men is on its way to rescue the narrator from being hanged.

When the narrator meets Policeman Fox, he is in a police station, hidden inside the walls of Mathers' house. Fox has Mathers' face, which reflects the narrator's guilt and fear over the murder he committed. Fox tells the narrator that he found the moneybox the narrator has been searching for, that it is filled with omnium, and that it is waiting for the narrator at his house. Fox also admits to creating 'eternity' as a joke on the other two policemen.