* Scéalaitheoir: This is a fairly straightforward and common translation, literally meaning "story-teller."
* Insitheoir scéalta: This translates to "teller of stories," and is a more descriptive option.
You could also use phrases that describe the *act* of storytelling, rather than the person, depending on the context. For example, you might say "duine a insíonn scéalta" ("a person who tells stories").
Therefore, Scéalaitheoir is a good starting point, but consider the context to determine if a more descriptive phrase would be better.