Ur-Peter was Peter's stone age ancestor, who is a parody of a basic caveman. He invented the wheel, however he couldn't seem to sell it, so he put his wife, Ur-Lois, up next to the wheel wearing nothing but a bra and panties to try and sell the wheels easier and it worked.
Moses Griffin was Peter's ancient Jewish ancestor, who is a parody of Moses from the Bible. He parted the Red Sea and saved the Jews. He also wrote the ten commandments, including that memorable one: "When we pass a billboard, please don't read it out loud".
King Arthur Griffin was Peter's medieval ancestor, who is parody of King Arthur. When Guinevere offered to make love to him if he could pull Excalibur from the stone, he asked her, "What if I can just move it an inch? Will you touch me?"
Ponce de León Griffin was Peter's explorer ancestor, who searched for the fountain of youth. Once he found it, he waded in it, and emerged from the water with the body of a baby, but his head (the only part of his body that didn't touch the water) stayed fully mature and grown. He reacted by saying, "That was worth the eight and a half year boat ride."
Nathaniel "Nate" Griffin was Peter's great, great, great, great Grandfather and a Black slave. He belonged to the Pewterschmidt family and was their stable boy. While working as a slave for the "massa", Nate peed in their cereal each day and had sex with Lois's great ancestor, Lois Laura Bush Lynne Cheney Pewterschmidt as well as her fine sister. He currently resides in Heaven where there is "a shortage of chairs". This might have implied he actually lived in hell.
Ulysses S. Griffin was Peter's great, great Grandfather, who is a parody of Ulysses S. Grant. In the cutaway, he is shown beating Robert E. Lee in a beer drinking contest, thus ending the Civil War. They compromised that there would be no slaves, but they wouldn't have to read.
Jabba the Griffin was Peter's great, great uncle, and is parody of Star Wars' Jabba the Hutt. He utters what sounds like "Rahsa Naba Doe-ah Gola Wookiee Nipple Pinchy!" He is arguably the fattest member of the Griffin family, and bears a resemblance to the boneless Peter in Family Guy Viewer Mail.
Angus Griffin was one of Peter's ancestors. He helped invent golf, agreeing with a bunch of other Scotsmen that they wouldn't allow Jews or Blacks to play the game. He has the same look as Mickey McFinnigan, Peter's true father.
Ella Fitzgerald Griffin is Peter's great aunt, who is a parody of Ella Fitzgerald. The cutaway shows her performing in a jazz club accompanied on piano by a young, sighted Ray Charles. When she sustains a high note during a scat solo, the champagne glass on the piano shatters, sending shards of glass into Ray Charles's eyes and causing his blindness.
Huck Griffin was Peter's great grandfather. He traveled with a friend named "N-Word Jim", who once became upset with Huck, when he called Jim a certain word which he believed was Jim's name. It is obviously a reference to Mark Twain's masterwork "The Adventures of Huckleberry Finn".
Juarez Griffin Peter's diminutive great grandfather who supposedly won a cock fight, beginning the Griffin winning streak. It is also possible that this might of created the ancient feud between Peter and Ernie The Giant Chicken.
Osias Griffin was also Peter's great grandfather. He was the owner of the 8th telephone ever made. His telephone number was 3. Apparently this wasn't easy enough, because at least once he has received a call for 7.
Peter Hitler was Peter's great uncle and brother of Adolf Hitler. He was always annoying to Adolf and interrupted him during his "Nazi stuff". He helped Adolf get great feedback from a rally, but this was also to Adolf's annoyance. It was also revealed that he shot Hitler and Eva Braun whilst playing with a gun, and, not wanting to get caught, made it look like a suicide.
Josiah Griffin was Peter's Grandpa, who helped design Bugs Bunny. He wanted to name the character "Ephraim the Retarded Rabbit", but nobody agreed on that name.
Thaddeus Griffin is Peter's evil brother. He shows up when Peter's mother leaves her husband, declaring this new event will surely affect his inheritance. Since he was not shown in a cutaway, he is definitely real, his appearance is based off the villain Snidley Whiplash from the Dudley Do Right segments in The Rocky and Bullwinkle show.
Kathy Griffin is Peter's famous cousin. Her never ending talking has led the family to attempt to sedate her with drugs, though their attempt failed when Chris drank from the glass meant for Kathy. This is obviously a relate to real comedian, Kathy Griffin.
Rufus Griffin was Peter's distant cousin, a black actor who starred in blaxploitation films such as "Caddyblack", "Blackdraft", "Black Kramer vs. Kramer" and "Black to the Future".
Peter the Pig is Peter's cousin (because of his last name being Pig, he might have no relationship to Peter) who's a parody of the three little pigs. He was shown trying to get the big bad wolf to stop blowing on his house.
Thomas Griffin was Peter's distant relative. He was a great philosopher. When his wife, Mrs. Thomas Griffin, asked him to find a job, he responded with the question, "Why?"
Stewie Cruise is Stewie's cousin (due to the lack of "Griffin" in his name, he may have no relationship with Peter), who is a parody of Tom Cruise. He appears on Oprah, repeatedly announcing that he is in love with Katie Holmes, and that he is not gay.
Quark Griffin is Peter's nephew. He is believed to be a Ferengi, meaning the Griffin family has had some relations with interstellar species.
Willie "Black-Eye" Griffin is one of the relatives mentioned in Untitled Griffin Family History. He was a silent movie actor with an odd voice that sounds like comedian Bobcat Goldwaith, who always got a black eye at the end of each sketch. Later in his series, it is revealed that Black Eye sounds just like Bobcat. He died when he got stabbed in a card game.
Peter Griffin Jr. is the deceased son of Peter and Lois. In The Juice Is Loose, it was shown in a cut away gag that the last time he was left with the kids, he accidentally killed him by shaking him too much (thinking it would stop making him cry, which, in a way, worked)
Griffin Peterson was Peter in a past life. He founded Quahog after being exiled to America by King Stewart. He was engaged to Lady Redbush and eventually married her.
King of Denmark Griffin was Peter's 14th century ancestor who suffered a heart attack at an enormous table and could not be attended to by a doctor in time. The resulting death of the Monarch is why the Danish build small tables.
Silas Pewterschmidt was an ancestor of the Pewterschmidt family. He bears an uncanny resemblance to Carter. He was one of the first to colonize America. He bartered with Native Americans by holding a knife to a baby's throat, presumably sparing its life in exchange for maize; an Indian word for corn.
Lois Laura Bush Lynne Cheney Pewterschmidt is Silas Pewterschmidt's daughter. She started an inter-racial family in secret with Nate Griffin. Their family back then looks exactly the same as the present day family, besides for them being black. She bears an uncanny resemblance to Lois Griffin.
Lillian Marie "Lil" Pewterschmidt was Lois's retired great aunt.