Who is The old tramp, the fake Merlin from That Hideous Strength and what is their importance?

When Merlin wakes, he steals clothes from an old tramp who had made camp for the night near where Merlin was sleeping. When the N.I.C.E. search party finds the tramp lying naked on the ground, they take him to be Merlin and bring him to the N.I.C.E. The tramp does not tell anyone he is not Merlin because they never speak to him in English because they think he is from centuries past. He takes advantage of the free food and beer he receives from the institute. Mark speaks to him without knowing who he is supposed to be, and the tramp and Mark form a relationship. Later, the tramp is used by Merlin to make the people in the N.I.C.E. believe he is a priest. The tramp eventually escapes after the N.I.C.E. begins to self-destruct.