Peter's age comes into question in "Baby, You Knock Me Out". Peter should turn 44 but no age is identified in the episode. In "The Tan Aquatic with Steve Zissou", Lois says that he's 43. Lois does say that she is 42 at this time, which would match the age difference stated in "Let's Go to the Hop" and ignore their both being 18 in "Meet the Quagmires". Lois herself would later turn 43 in "Lois Comes Out of Her Shell".
Similarly to Archie Bunker from All in the Family, Peter appears to be unintelligent and is consistently depicted as crude and lowbrow. He enjoys activities such as going to up-market tailors and farting inside the suits. His favorite pastime is watching TV. He is also very cantankerous at times and has a strong jealous streak in regards to Lois. A running gag on the show is Peter's preference for Pauly Shore movies over classic films such as The Godfather and Citizen Kane. He is also a huge KISS fan and followed them during the KissStock shows and even got a copy of Kiss Saves Santa for Christmas. Peter is also an ardent fan of Barry Manilow, though this is a fact he has been known to deny in public. Peter also mentioned that he enjoys the following breakfast cereals: Total, Trix, and Boo Berry. Peter has demonstrated himself to be an avid television fan, with his favorite shows consisting of Star Trek, Three's Company and Charles in Charge.
An I.Q. test in "Petarded" confirms that his low intellect places him in a category below mentally retarded. He rushes off to attend Quahog College just to count to three in "3 Acts of God". His mental shortcomings have resulted in various accidents to other people; most notably the death of his step-father Francis Griffin, and injuries on multiple occasions to his wife Lois. His attention span is also incredibly short. When he discovers his mental retardation in the episode, he closes his eyes while driving, wishing "it would all be over" and hitting Tom Tucker with his car instead. Given his short attention span, as well as his erratic and frequently inappropriate behavior, it is conceivable that Peter suffers from Attention Deficit Hyperactivity Disorder, or ADHD. In addition, Peter is often seen getting hurt mostly by his own fault. When trying to impress Chris with his forward-thinking, Peter claims it is still 1998 in "Baby Got Black".
Peter also has a habit of proving his masculinity, not wanting Lois to fall for another man. He is incredibly jealous of other attractions Lois has in her life, an attitude that tends to get out of hand in most cases; in "Stuck Together, Torn Apart", he goes so far as to punch his reflection in the mirror after Lois comments on it being handsome. In "Brian Sings and Swings", he tells Lois, "Remember what I always tell you, if I come home in the middle of the day and catch you having sex with someone, I'll kill you both" though when he catches her in bed with Bill Clinton in "Bill and Peter's Bogus Journey", he takes no hostile actions whatsoever. However, he seems not to mind the fact that she slept with other men before they met, just so long as she doesn't do so again; he is particularly proud of the fact that she once slept with Gene Simmons of Kiss when he discovers this in "Road to Europe", but forbids any sexual activity between the two now as seen in "Don't Make Me Over".
Peter seems to find it frustrating that he is "wrong" while Lois is "right" about issues all the time, and apparently takes these issues competitively, just waiting for the day she slips up. This day finally comes in "PTV" after settling a conflict with Lois about censorship on television that she appeared sure to win. In an ironic twist that forces Lois to concede defeat, Peter celebrates by opening a secret compartment within the ceiling containing balloons, streamers, confetti, and a banner reading "PETER'S RIGHT!"; Peter then claims that he set this up 15 years ago, suggesting that this had been a pretty major issue for him for quite some time. Curiously, in the non-canon episode "Da Boom", after Lois admits he was right about the end of the world and she was wrong, Peter makes no reference to the compartment, though he had been bragging about his "victory" for two weeks straight. Maybe the compartment had been damaged in the nuclear devastation.
Among the members of his family, he tends to treat Meg with the least respect; in "Peter's Daughter", for example, he reminisces about the various pranks he played on her, including tripping her, flicking her nose with his finger, and even shooting her at one point. Also, he wipes a boogie on her hat saying "Hey Meg...Proud of you". He is known to embarrass her at times and with things that mean the most to Meg; the entire family once huddled together to read her diary and continue after Meg catches them. However, later episodes of the series show Peter developing greater respect and unity between himself and his daughter such as in "Road to Rupert" and the aforementioned "Peter's Daughter", though these moments tend not to last for very long.
"I Dream of Jesus" reveals that his favorite song is the Trashmen's "Surfin' Bird", and loves the song to the point of repeatedly singing it, playing the record of it, and trying to convince others that "the bird is the word". In "Wasted Talent", a running gag debuted when someone, usually Peter, will be running and fall and then hold his shin exclaiming the sound "Ssss Ahhhh" once or multiple times.
Peter's best friends are Glenn Quagmire, Joe Swanson, Brian, and Cleveland Brown prior to his moving to Stoolbend, VA. They enjoy hanging out at their local bar, The Drunken Clam, drinking and chewing the fat. The four men (often without Brian, although he has joined them on several occasions) do many things together. Once the four friends entered and won a costume contest at an 80s TV convention, dressing up as the A-Team. On another occasion, their fishing boat was wrecked, and they were stranded together on a desert island. Peter also has other friends such as Mort and Muriel Goldman and nudists Dave and Dotty Campbell, with whom he is seen occasionally. He became friends with Brian's ex-girlfriend Jillian, which stems from their below average intelligence; she even asked him to give a speech on her wedding.
- Peter took trombone lessons in junior college. He plays the trombone during Chris' open house in "Fast Times at Buddy Cianci Jr. High".
- Peter was able to pilot a blimp over the Super Bowl, to return his fraudulently obtained welfare payments. In addition, Peter managed to obtain his own helicopter, the 'Petercopter' and an airship 'Hindenpeter'. Peter also gained a Pterodactyl called the Peterdactyl in "Quagmire and Meg" and a giant boomarang called the Peterang in "Livin' on a Prayer.
- Peter was born in Mexico, as revealed in "Padre de Familia".
- He played the song Rock Lobster on his guitar to cheer up Cleveland when his wife was having an affair and had kicked him out of the house in "The Cleveland-Loretta Quagmire". Together Lois, who played the mandolin, and Peter on guitar formed the duo "Handful of Peter" in "Deep Throats" in their younger days. In "Padre de Familia", accompanying himself on the guitar, Peter sings a brief paeon to the USA, "What America Means To Me", in a USO concert, as a tribute to the troops.
- According to "Peter, Peter, Caviar Eater", Peter collects Star Wars collector glasses, confirming Peter as a Star Wars fan Also - he mentioned he collects Star Wars trading cards in "Screwed the Pooch".
- Peter's farts are particularly powerful and noxious. In "Let's Go to the Hop" and many other episodes, they make people vomit, and in "Screwed the Pooch" caused Peter himself to pass out after he farted while in a sealed box. He was also known to have had out farted Michael Moore in a restroom in 'The Perfect Castaway". However, this more resembled a duet between the two, resembling the song "Dueling Banjos" from the film Deliverance.
- He can play the piano perfectly provided he is drunk in "Wasted Talent".
- Peter won the "Most Ticks" award in 1965 shown in "He's Too Sexy for His Fat".
- In The Simpsons episode "The Italian Bob", Peter is seen in the Italian police book that Peter is wanted for "Plagiarismo" which means copying someone's work.
- The James Woods Regional High School Yearbook was dedicated to Lando Griffin, Peter's alter ego in "Let's Go to the Hop".
- In "Dammit Janet!", Peter encouraged Lois to become a flight attendant, so that he could travel free as a spouse, enjoying journeys to places as far away as Australia and Kentucky.
- In The Cleveland Show episode "BFFs", his cell phone voice mail greeting is the automatic greeting using the name "Dick Poop" and laughing. In "Cool Hand Peter", his ringtone is the theme to The Cleveland Show.
- He has an iPhone, as revealed in "Seahorse Seashell Party" that he uses to hum the opening theme to Indiana Jones and the Last Crusade.
- It is hinted that Peter has a small penis. In "Be Careful What You Fish For", Peter came out the shower and the dolphin Billy Finn made fun of it. And in "You Can't Do That On Television, Peter", while Peter babysat Stewie he compared their size and Peter was bummed out. In the uncensored version of "Airport '07", an image of Peter's Penis is actually shown, during the DVD commentary of which, producer Danny Smith remarks on it being "three and a half inches of Irish man-meat." However, in the mock DVD commentary of "Road to Rhode Island" in the Family Guy: The Freakin' Sweet Collection DVD, Stewie launches into an elaborate story involving Peter actually having a large penis.
- Peter's twitter name is "PumpkinEater69" in "Friends Without Benefits".
- Peter notes that Lois is unhappy because he shook Stewie, resulting in his unusual gait in "The Giggity Wife". Peter had previously shaken Peter Griffin Jr., seen in "The Juice Is Loose", resulting in his death.
Peter first met Lois while he was working as a towel boy for Marguerite Pewterschmidt. He worked at the Happy-Go-Lucky Toy Factory for the bizarre Mr. Weed for the first three seasons of the show. But when Mr. Weed was accidentally killed by choking on a dinner roll on which Brian had originally been choking, Peter was out of a job and had to find work elsewhere.
To date, Peter has been employed as a toymaker, knight and a fisherman. In "The Perfect Castaway" during a desperate attempt to catch more fish at a private island, Peter's boat is destroyed by a hurricane. Despite surviving the hurricane, with the loss of his boat, Peter is again jobless. In "Jungle Love", Peter goes to the unemployment office, and obtains a job at the Pawtucket Brewery. Initially he is placed on the line, but after over-indulging in the free ale, he is demoted to the shipping department, working with Opie and under Angela.
In a running gag, storylines are interrupted by unexpected fights between Peter and a giant chicken. These battles feature long strings of action film-style sequences, with explosions, high-speed chases, and excessive collateral damage to both property and innocent bystanders, ending with Peter the victor leaving the giant chicken for dead, only for a sudden movement to show that the chicken is still alive.
In "Da Boom", the feud starts over a trivial incident where the chicken gives Peter an expired coupon at the grocery store. The fight resumes in "Blind Ambition". In "No Chris Left Behind" the chicken is identified as "Ernie", and he has a wife named Nicole, also a giant chicken. Peter is invited to dinner with them after they realize that their fighting is pointless, but then they argue over who will pay the bill, and the fighting starts all over again. Ernie makes a brief, non-fighting appearance in "Meet the Quagmires", in which Peter unwittingly assaults the giant chicken at an 80s dance, retroactively providing Ernie with a grudge against Peter. Ernie the chicken appears in the Star Wars parody episodes Something, Something, Something, Dark Side and It's A Trap!, as the infamous bounty hunter Boba Fett.
Ernie was also mentioned in "New Kidney in Town". When Peter was hospitalized due to kidney failure, Brian offered to give Peter his kidney. In response to the family's shock, Dr. Hartman stated that this transplant was not the only crazy thing that took place in medical research, and said that he once attempted to clone a chicken. This resulted in the original chicken to grow human-sized, violent, and incredibly hostile. Peter paused at this, and stated "we need to have a talk later."
Ernie appears in the video game as the final boss.
Despite being obese, a heavy drinker, and accident-prone, Peter appears to be in great health. Periodically, in typical cartoon fashion, Peter is shown recovering quickly from serious injuries, such as losing all the fingers on his right hand while handling M-80 firecrackers. In spite of the injury, he has no visible scarring on his hand. In some episodes he displays enormous strength, such as when single handedly challenging a professional football team in "Patriot Games". According to "The Father, the Son, and the Holy Fonz", Peter played high school football.
Peter asserts that he weighs 293lbs in "Vestigial Peter", the same as he did in grade school. In "Spies Reminiscent of Us", during Peter's "poop montage", he loses over 50 pounds; going from around 330 lbs to 270 lbs.
He underwent a vasectomy in "Sibling Rivalry".
Episodes like "Mr. Saturday Knight", "Model Misbehavior", "Deep Throats", "Peter's Two Dads" and "April in Quahog" show that Peter has used various drugs such as LSD, Meth, "ecstasy", marijuana, steroids, cocaine, and crack cocaine, but has managed to avoid incarceration and long-term effects from the use of these drugs.
In "McStroke", after eating thirty hamburgers in one sitting, Peter suffered a stroke that paralyzed the left side of his body. For the next three months he walked with a limp, his arm and leg hung lifelessly from his body, and his eye and part of his mouth had slid down his face, giving him a speech impediment. This damage was reversed completely after a five minute session at a stem cell research facility.
In "The Fat Guy Strangler", Peter's mass causes him to have his own gravitational pull, shown when Brian threw an apple, a glass of water, a book and a Television, which immediately started to orbit his body.
In "Not All Dogs Go To Heaven", Peter reveals as a child he was never immunized for the mumps.
In "New Kidney in Town", Peter suffers a kidney failure from a homemade energy drink. Brian offers do donate his kidneys, which would kill him. Before the surgery, Dr. Hartman offers to give up one of his kidneys, which he does and reveals that Brian's kidneys could not of been transferred to Peter's body.
Peter is shown generally to be a complete idiot, such as being dumb enough in "Stew-Roids" to think that there can be a World War 5 before World Wars 3 and 4 because it would be so intense that it would "Skip right over the other two.". In "Petarded", after winning a game of Trivial Pursuit which Lois rigged with questions from the Pre-school edition so he could win, he thinks that he is a genius, and at Brian's prompting he takes an exam to apply for the MacArthur Genius Grant, which he fails so awfully that he is found to be mentally retarded. In "Quagmire's Baby", Peter thinks that babies can be aborted whether they're born or not.
Peter has shown some sparks of being smarter than those around him, such as in "Back to the Woods" when James Woods returns to get revenge, Peter and Brian get rid of him exactly the same way they did the first time, using a box and trail of candy, he makes a point that next time Woods shows up they should do that in the beginning as he has already fallen for it twice.
Peter does have ideas he thinks are smart but often back fire, such as in "FOX-y Lady" when he got his new drivers license he decided to have the picture taken when he was drunk, so if a cop pulled him over for DUI when he looked at his license he would think he was just fine.
Also despite being married to Lois for 20 years, he was unable to realize she was in danger in "And Then There Were Fewer" despite her acting very odd. As well as was more interested in listening to his songs than to pay any real attention. He also firmly believed that Derek Wilcox was a god due to the fact the picture on his phone made him look as if he was holding up the Hollywood sign, despite Derek clearing explaining to him it was merely a camera trick.
Peter's car strongly resembles a 1975 Ford LTD Station Wagon  although no specific brand has been mentioned and in the commentary for "Road to Rupert" there is a remark about it having a flip-down TV in a mid-'80s station wagon.