<Li> Francis Griffin (voiced by Charles Durning)--Peter's grumpy and stubborn adoptive father, Lois's adoptive father - in - law, and the adoptive paternal grandfather of Meg, Chris, and Stewie . He was once married to Peter's biological mother Thelma Griffin . An obsessively devout Roman Catholic, he hates Lois because she is not a Catholic, and often calls her a "Protestant whore", disapproves of his son's family's lifestyle, and frequently attempts to force his religious views on them . To a lesser extent he disapproves of Lois due to her heritage, and is angry with Peter for not marrying an "Irish rose". When Peter and Lois got married, Francis taped the sign "To a Protestant Whore" underneath the "Just Married" sign on the limousine . Despite all of this, he truly did love and care for Peter, and showed on multiple occasions to care for his grandchildren . Francis used to have a job at a metal fabrication plant; after his short retirement, he became a bodyguard for the Pope . In the episode "Peter's Two Dads", Francis dies on Meg's 17th birthday when Peter (dressed up as a clown) gets drunk and tries to ride a unicycle down the stairs, but ends up falling off the stairs and landing on top of Francis . Francis dies in a hospital after uttering "Peter...you're a fat stinking drunk!" as his last words . Francis appears at the memorial in "Perfect Castaway". In "Family Goy", Francis appears as a ghost where he tells Peter not to convert to Judaism . </Li> <Li> Mickey McFinnigan (voiced by Seth MacFarlane)--Peter's biological father, making him the biological paternal grandfather of Meg, Chris, and Stewie, and father - in - law of Lois . He is an Irish drunk . He reprises a major role in "Peter's Two Dads", when Peter visits him in Ireland . Mickey mocks Peter at first and bullies him, but Peter challenges him to a drinking contest and wins . Finally, Mickey accepts Peter into his family and spoils him ever after by buying Guinness and more . </Li> <Li> Thelma Griffin (voiced by Florence Stanley in the first appearance, Phyllis Diller in later appearances, Alex Borstein as a young woman in "Don't Be a Dickens at Christmas")--Ex-wife to Francis, mother of Peter, and paternal grandmother of Meg, Chris, and Stewie . She is the mother - in - law of Lois . She first appears in "Holy Crap". She is 82 years old as stated in the episode "Mother Tucker", has gray hair and noticeable wrinkles below her eyes, and wears purple earrings and a purple bead necklace . She also wears glasses like her son and husband and is a heavy smoker . Unlike Francis, she is generally friendly and personable, and gets along well with Lois . Before Francis' death, she divorced him because she had "needs he didn't fill" and dated Tom Tucker for a while in "Mother Tucker". She often appears with news inconvenient or troubling to Peter and his family . Her brief partnership with Peter's biological father, Irishman Mickey McFinnegan, is only established in the episode "Peter's Two Dads". In the episode "Grumpy Old Man", it is revealed that Thelma was sent to a retirement home . In the Season 12 episode "Mom's the Word", it is revealed that Thelma died from a stroke . Thelma's death was written into the series because of Phyllis Diller's own death in August 2012 . </Li> <Li> Karen "Heavy Flo" Griffin (voiced by Kate McKinnon)--Peter's older sister who first appears in "Peter's Sister ." She is the paternal aunt of Meg, Chris and Stewie and sister - in - law of Lois . Karen is a professional wrestler and is shown as the reason Peter bullies Meg where he was picked on by Karen . During her fight with Peter in the ring, Karen was knocked out by Meg using a real folding chair instead of a fake folding chair which puts her in a coma . At the end of the episode a doctor calls Peter on the phone and tells him that Karen needs a blood transfusion to save her but Peter refuses . </Li>

Who plays peter's mom in family guy