Who is Seymour Glass from Nine Stories and what is their importance?

Seymour Glass is a young soldier who has returned from World War II a deeply changed and troubled man. He has been hospitalized as a result of his mental state, but he has now been released. Seymour's behavior continues to be strange and inappropriate. His unusual actions are only hinted at in the story, but he has apparently wrecked his father-in-law's car by deliberately driving it into a tree, given his wife a book of poetry in German expecting her to learn the language so she could read it, and has done something unspecified to her grandmother's chair. His in-laws are concerned that he may try to harm their daughter. In the end, Seymour takes his own life.