Who is Jeff Gulden from One True Thing and what is their importance?

Jeff Gulden is the middle child in the Gulden family. He is twenty-years-old and has auburn hair, resembling his mother. He has always felt as if he was living in Ellen's shadow, but they still have a close relationship even though he is envious of her. Jeff struggles to speak with his father after his mother's death, but remains the linchpin of communication within the Gulden family after Ellen is arrested. When Ellen is acquitted of murdering their mother, Jeff is the one who picks her up and drives her back to New York. Jeff is also the only one who ever stuck up for Ellen in her terrible relationship with Jonathan.