He was once married to Peter's biological mother Thelma Griffin. Francis Griffin (voiced by Charles Durning) – Peter's grumpy, stubborn and abusive 80-year-old adoptive father, Lois's adoptive father-in-law, and the adoptive paternal grandfather of Meg, Chris, and Stewie.The characters listed below are the extended family of the Griffin family that come from either Peter's side of the family, Lois's side of the family, and the occasional members of Brian's family:

Brian Griffin (voiced by Seth MacFarlane) is the family's ten-year-old anthropomorphic talking white Labrador Retriever and the best friend of both Stewie and his father Peter.