Dr. Mason is a Professor of Ancient Greek, and was the father of Angela Mason.
When Sam and Dean discover the area around Angela Mason's grave to be dead, they learn her father is a professor at a local school and go to question him. They arrive at his office under the pretense of being friends of Angela's and offer their condolences to him.
Later when Sam and Dean discover ancient Greek symbols used for necromancy carved in Angela's coffin, the Winchester's return to Dr. Mason's office and an angry Dean begins to accuse Dr. Mason of bringing his daughter back from the dead. Dr. Mason calls Dean insane and tells the brothers to leave his house, threatening to call the police.