Mark Carter, brother of Samantha Carter and the son of Jacob Carter, had long been estranged from his family. When Mark and Sam were young, their mother had died in a tragic automobile accident for which Mark had always blamed his father. He grew distant, losing touch with both his father and his sister for many years. Mark resides in San Diego with his two children, a son and a daughter. After Jacob had become a Tok'ra, it was at Selmak's urging that both Jacob and Sam visited Mark in San Diego. Their visit began a reconciliation, and the family began keeping in close touch. In fact, it was through her brother that Sam was introduced to Mark's friend, Pete Shanahan, a policeman from Denver with whom she developed a relationship.
Cross Reference: Jacob Carter, Samantha Carter, Pete Shanahan
Episode Reference: Seth