Mark Rein·Hagen (born 1964), often written as Mark Rein-Hagen, is a game designer who has contributed to role-playing games, card games, video games, and board games. He has contributed extensively to American gaming company White Wolf. He is perhaps best known as the creator of Vampire: The Masquerade and its associated World of Darkness games. He was also along with Jonathan Tweet one of the original two designers of Ars Magica.
He has been living in Tbilisi, Georgia.