Ethan Frome cannot possibly be a fully developed character in the novella, Ethan Frome as he is not a fully developed man. Thwarted in every direction by his dominating wife, Zena, whose shadow is everywhere, no more so then when she is not physically present and Mattie and Ethan cannot even bring themselves to look at her chair nor the cat for they both seem to have her eyes.
Ethan might have a history, as n12 says. He is indeed the protagonist, and he is sensitive and mythical and deep however he is certainly not complete. For he is missing his masculinity which has been so ruthlessly stripped from him by his wife and is also missing the gentle sweetness of love through which he feels he will find satisfaction. His attempts to find this with Mattie further his character as a broken man, bringing it into the physical world. However, a complete character is one who is whole and textered and perhaps, fulfilled which are all qualities which Wharton has not bestowed upon Ethan.
One might compare Ethan Frome to a background actor, one who is always there, but never evident. His family have lived on the same farm for generations - and died there. There is no progress, no boastings, no strength. Just weakness, and to be a weak protagonist is to be undeveloped. We never do discover Ethan's full strength which is part of what makes Edith Wharton's story so magical.
Ethan Frome, in my opinion is a fully developed character.This is because most part of his story is indirectly an image of the vision the narrator of the novel has.In the beginning of the novel, the narrator clearly states"It was that night that I found the clue to Ethan Frome,and began to put together this vision of his story"(pg. 15).
Even when we read the story of his life, we do have the knowledge of major parts and phases of his life though we may not posses the knowledge of inconspicious fragments of his life.
We know much about him: he is the protagonist of the story, is a farmer whose family has lived and died on the same Massachusetts farm for generations. A sensitive figure, Ethan has a deep, almost mystical appreciation of nature, and he feels a strong connection to the youth, beauty, and vital spirit of Mattie Silver, his wife’s cousin. However, he ultimately lacks the inner strength necessary to escape the oppressive forces of convention, climate, and his sickly wife.