Dean Thomas is a wizard in the same year as Harry Potter and in the same house: Gryffindor. He is very artistic and usually designs banners for Quidditch matches and for Gryffindor in general. His best friend is Seamus Finnigan.
Dean doesn't know who his father is, as he left him when he was a baby, and so doesn't know if he is a half-blood or a Muggle-born wizard, and is therefore hunted down in Deathly Hallows. In truth, his father was a wizard who fought in the first war against You-Know-Who (Lord Voldemort) and left his family to protect them, never telling them that he was a wizard in the hope that it would keep them safe and well.