Dean’s parents, who didn’t know anything about any deaths at Hogwarts as of the beginning of the 1995 – 1996 school year, because their son didn’t see fit to tell them (OP11). Mr. Thomas is Dean’s stepfather; Dean’s biological father was a wizard who was killed by Death Eaters (JKR).
Other canon notes and references
J. K. Rowling shared much about Dean Thomas's background on her Official Site - read it here.
Dean is from what he always thought was a pure Muggle background. He has been raised by his mother and his stepfather; his father walked out on the family when Dean was very young. He has a very happy home life, with a number of half-brothers and sisters.
Tags: family tree