A show called Family Guy is guaranteed to have plenty of family-related storylines and such is the case with Seth McFarlane's critically-acclaimed FOX animated sitcom. Though the spotlight mostly remains on Peter, his wife Lois, his dog Brian and the children, the family tree is quite extensive. In this world, even Leonardo Da Vinci is related to the Griffins.
Several blood relatives pop up from time to time in the sitcom and they are not always likable. From gambling addicts such as Thelma to evil billionaires such as Carter, there is never a shortage of drama whenever the Griffin relatives are around. And with the show still running, more relatives are guaranteed to show up in the future.
Carter Pewterschmidt
Lois' rich father is the kind of billionaire people love to hate. He has conservative views and doesn't approve of introverted people. Carter also tends to be violent towards his son-in-law Peter.
At one time, he offers Peter $1,000,000 to not marry Lois because he feels she deserves someone better. He also treats his billionaire friends very badly. He tries to hit on Ted Turner's wife and shows off his iPod every time he is with Bill Gates.
Karen Griffin
Peter's never-heard-of-before wrestler sister Karen Griffin shows up for Thanksgiving dinner in Season 14. She greats him with a fart on the face and finds it funny. It soon becomes apparent that Peter has never liked her. He laments about her presence, stating that she always takes advantage of the fact that she is a wrestler to bully him.
As the family has dinner, Karren embarrasses Peter by telling everyone the childhood stories he never wanted people to know about. She also knocks him out during a family football game. When she gets hospitalized, Peter refuses to donate an organ to her as payback.
Bertram
Bertram is born to a gym teacher and her husband after the couple is accidentally allocated sperm that belongs to Peter Griffin. The gym teacher thus gives birth to a baby that resembles Stewie and names him Bertram.
Bertram begins a rivalry with Stewie as soon as he is born. The two fight over the position of King Of The Playground but Stewie ends up winning. Bertram also goes back in time to kill one of Stewie's ancestors so as to erase Stewie from existence. Luckily, Stewie manages to defeat him before he can cause any major harm.
Thelma Griffin
Peter's mother Thelma apparently had a penchant for throwing whisky bottles at him whenever he complained of toothaches as a child. She also enjoyed insulting him because she felt he was worthless.
The Griffin family hates her so much that they have installed a rocket escape pod inside the house that they can use to flee whenever she comes around. Thelma's gambling addiction has gotten the better of her as she spends most of her days in Vegas. Perhaps the worst of her deeds is cheating on 'Peter's father' and lying to him that Peter was his child.
Larry
Larry is also a result of Peter's past as a sperm donor. He comes to see Peter and during a backyard dinner party, he begins flirting with Lois. She states that he reminds her of a younger Peter. Within no time, the two end up kissing.
Later, Peter catches Larry trying to unclasp Lois' brassiere as he gives her a back rub. He confesses that he is in love with her and reveals that they shared a kiss. This angers Peter who goes on to fight with him. Larry has the upper hand during the fight but Lois saves Peter by knocking him out with a flower pot. She then reassures Peter that she loves him.
Peter's Hairless Twin
Simply known as Peter's Hairless Twin, Peter's brother shows up when Carter names Chris as the sole heir of his fortune. Carter does this as appreciation after Chris nurses him for a while.
When Peter confronts his hairless twin with a shotgun, the twin shoots him instead. He then comes into the house and introduces himself as the new head of the family. He is looking forward to enjoying the fortune that Carter will leave Chris, though he isn't aware that Chris has declined it.
Francis Griffin
Francis Griffin is the man Peter thought was his father for a long time before Thelma revealed that she cheated. This makes him Peter's step-father. Francis is a devout Catholic who hates protestants. During Peter's wedding, he taped a sign stating "To A Protestant Wh**e" under the one stating "Just Married."
At one point, he hits Brian with a bible for asking him hard questions. When he attends Meg's birthday party, he only brings her a single cookie as a present.
Patrick Pewterschmidt
Lois' older brother, Patrick, is psychotic. Her parents keep him a secret from her for 30 years hence she lives most of her life not knowing he exists. When she finally learns about him, she vows to be there for him. She frees him from the penitentiary in which he is being held and brings him home.
This turns out to be a mistake as Patrick becomes a serial killer called the Quahog Strangler. He nearly kills Peter too but is arrested and sent back to prison.
Dylan Flannigan
Dylan is quite the juvenile delinquent. He is a child that Brian never knew he had. Brian learns that his one-night stand with Tracy resulted in Dylan being born but she never told him about it. When Brian visits Tracy, she finally tells him about Dylan and asks the two to leave together so that they can catch up and bond.
Sadly, Dylan proves to be a nuisance. He acts disrespectfully towards the Griffin family and even beats up the evil monkey when it comes out of the closet. A fed-up Peter then convinces Tracy to take her son back.
Mickey McFinnigan
Peter's Irish biological father shares some traits with him but he is worse. While both of them love drinking, Mickey is an addict who has garnered a reputation as a town drunk. Apparently, Thelma had a one-night stand with him during a visit to Ireland. The short affair resulted in Peter being born.
Just as Peter has a talking dog named Brian, Mickey also has a talking sheep name, O'Brian. He also has an unkempt beard and messy hair. Mickey even forces Peter to drinks several bottles of beer to prove that he is his son.