Who is the protagonist "The Signal-Man" and how does he change?

The protagonist is actually the anonymous narrator who
meets the signal man and becomes involved in the fascinating story that the signal-man
tells him. We don't actually know much about the protagonist: we are never told his
name, and we know nothing of his occupation or way of life, except that he obviously
likes to walk. However, what we can see as the story progresses is the way in which he
changes through the course of the narrative.

Note the way
that he responds to being told about the first ghostly apparition that appears to the
signal man, and how he works to discount it:

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Resisting the slow touch of a frozen finger
tracing out my spine, I showed him how that this figure must be a deception of his sense
of sight; and how that figures, originating in disease of the delicate nerves that
minister to the functions of the eye, were known to have often troubled patients, some
of whom had become conscious of the nature of their affliction, and have even proved it
by experiments upon
themselves.

The narrator is
keen to find a reasonable explanation for the supernatural events that the signalman
relates. He stresses science and advances in our understanding to reassure both himself
and the signalman. However, in spite of this stance that the narrator takes at the
beginning of the story, it is clear that at the end, the horrifying events concerning
the signalman's death have convinced the narrator, as he points out the various
coincidences that stress the truth of the ghostly apparitions. He has moved from
incredulity to reluctant and terrified belief.