Dean shares a Gryffindor dorm with Harry, Ron, Neville, and Seamus Finnegan. He and Seamus are best friends. Dean is a decent guy who tries to mediate between Harry and Seamus when they are fighting about the Daily Prophet and whether or not Harry is crazy. Since Dean comes from a Muggle family, he seems a little more levelheaded about these questions: he just wants to keep his head down and continue going to Hogwarts. Dean has one dangerous moment when he actually asks Firenze, "Did Hagrid breed you, like the Thestrals?" (27.31). Fortunately, as soon as Firenze looks at Dean, he realizes how offensive his question was and apologizes. Which is probably why Dean is still alive at the end of Book 5.