The narrator is an engineer who has come to Starkfield to work at a nearby power plant. He's an educated, upper-middle-class man who happens to become fascinated by the figure of Ethan Frome, 24 years after the tragic sled ride.
Luckily for us, the narrator is a kind of a nosey guy. He feels completely comfortable going around asking everybody he sees to tell him Ethan's story. One question to ask is whether the narrator is exploiting Ethan for his own amusement or is he just fascinated by Ethan and his story? We're not entirely sure what his motivation is, but we prefer to look at the narrator as a man who identifies with Ethan and feels that his story needs to be told.
For more on the narrator, check out "Narrator Point of View."