narrator

n. person who narrates; storyteller; one who reads narration or descriptive text in between the acts of a play (also narrater)

For information about the software by Microsoft, see Microsoft Narrator.A narrator is an entity within a story that tells the story to the reader. It is one of three entities responsible for story-telling of any kind. The others are the author and the reader (or audience). The author and the reader both inhabit the real world. It is the author's function to create the alternate world, people, and events within the story. It is the reader's function to understand and interpret the story. The narrator exists within the world of the story (and only there—although in non-fiction the narrator and the author can share the same persona, since the real world and the world of the story are the same) and presents it in a way the reader can comprehend.
See more at Wikipedia.org...

Noun
1. someone who tells a story
(synonym) storyteller, teller
(hypernym) speaker, talker, utterer, verbalizer, verbaliser
(hyponym) anecdotist, raconteur
(derivation) tell, narrate, recount, recite

(n.)
One who narrates; one who relates a series of events or transactions.
  

an advocate.