We don't really learn anything about Dick Humbird in this novel apart from the fact that Amory Blaine admires him at first sight. As we learn from the text:
Dick Humbird had, ever since freshman year, seemed to Amory a perfect type of aristocrat. He was slender but well-built—black curly hair, straight features, and rather a dark skin. Everything he said sounded intangibly appropriate. (1.2.352)
Unfortunately, Dick dies in a car accident while going to Princeton. His death fills Amory with a sense of his own mortality, and Amory even hallucinates about Dick coming to visit him years after his death. Then again, it might not be a hallucination, since Tom D'Invilliers seems to see Dick too. Dick is in this book to remind us that no matter how young and awesome we think we are, the Grim Reaper is going to come for us one day.
Yeah, dudes—we told you this book was as bleak as a November day in North Dakota.