Jeff was brutally beaten by Stan's boss, Avery Bullock in "Bullocks To Stan". He has also recovered from being crushed under a heavy object in "Phantom of the Telethon" and having all his skin peeled from his body by Roger in "Love, American Dad Style".
Until "Joint Custody", Jeff had not spoken to his father for years and "his mother ran away before he was born". In that episode, he went to his father Henry Fischer's farm in Raleigh, North Carolina, when trying to escape from Stan and Roger. Jeff is wanted in Florida for possession of marijuana as he had skipped bail.
In "Daesong Heavy Industries II: Return to Innocence", a navy carrier captain believes that Jeff may be his long-lost illegitimate son, and carries a photo in a locket of a woman that bears a striking resemblance to Jeff.
In "Naked to the Limit, One More Time", Jeff discovers about Roger being an alien and Stan has to kill one of them so the CIA wouldn't find out and risk his family. When Roger asks Jeff for a hug before he leaves, Roger tosses him into a tractor beam from a ship sent to pick him up from his home planet which takes Jeff away, leaving a stunned Hayley behind.
In "Lost in Space", he is forced to reveal the trickery of Emperor Zing in hiding true love from his people, setting off a revolution and escapes in a spacecraft, looking for a way to get back to Earth and to Hayley.
In "The Longest Distance Relationship", Jeff is able to communicate with Hayley though a CB radio and discovers a way to return to earth through a wormhole, but arrives 60 years in the future and learns that he cost her a chance to have a great life with Millionaire Matt Davis. Unhappy with having upset the family and giving the elderly Hayley a heart attack, he returns through the wormhole and tells the again-young Hayley to move on with her life as he sadly gives up on her, unaware that Matt is killed by Roger very shortly after.
Jeff appears to return from space in "Holy Shit, Jeff's Back!", but he acts strange, causing Hayley some doubts, although his new attitude soon wins over Stan. In reality, he is an alien named Zebleer from a species that "collects" and he has come to sample more earth items, his race having dissected Jeff in order to find out more about him. Hayley and Roger board the alien mothership and find that the real Jeff has been killed previously and when they are captured, they are due to be next. Having bonded with Stan over froyo, Zebleer confesses what is going on and escorts Stan to the ship to save Hayley, noting that the froyo makes mankind worth protecting. When Hayley rejects his direct offer to replace Jeff, he instead elects to have Jeff's brain put in his body, trading his life. As they return to earth, Roger informs them that they will have their memories erased when they depart the spaceship, leaving them unaware that Jeff is no longer entirely human.
When Jeff and Hayley decide to have a baby between episodes "Bahama Mama" and "Roger's Baby", they find they cannot get pregnant due to Jeff's alien physiology. Roger becomes a surrogate to "re-birth" Jeff into a fully-human adult, although a hormonal imbalance nearly causes Roger to flee with the embryonic Jeff and rename him "Tristen." After the situation is resolved, Jeff is reborn as fully human, although he decides he is too young to have a child.
He is known to be a 'stoner', and lived in his van for some time.
He seems to be extremely easy going; He was dumped by Hayley in "Bullocks To Stan" for being a push-over. However, Stan taught him to stand up for himself by beating, electrocuting, and entombing him and they got back together. In addition, the Jeff and Hayley break up became some sort of annual tradition on American Dad!. Episodes noting the break up include the aforementioned "Bullocks To Stan", "Haylias", "Dungeons and Wagons" and "Pulling Double Booty".
Jeff also appears to care very much for Hayley, as revealed in "For Whom the Sleigh Bell Tolls", as he tells this to Stan when he heals him. In "Lost in Space", he was willing to put his privates on the line to prove that his love for Hayley is real.
- Jeff is based on Seth MacFarlane's friend, also named Jeff Fischer, who voices the character.
- Jeff tells Hayley that he was born in the front seat of his van where she is sitting in "Stan Knows Best".
- In "The People vs. Martin Sugar", it is revealed that if he does not smoke weed, Jeff masturbates constantly.
- In "100 A.D.", it is hinted that Jeff smells like cheap weed and applesauce. Also in the same episode, his van has the ability to shed its cover and turn into a version of Chitty Chitty Bang Bang, which he shows to Hayley after they get married. Also, according to Jeff, he has a small penis.
- In "The Unbrave One" it is revealed that Jeff has a younger brother that their dad likes better.
- Until the events of "Naked to the Limit, One More Time", he remained unaware of Roger being an alien. Previously in "Dr. Klaustus", he believes that Roger is attracted to him.
- In "Stan's Best Friend", it's revealed that he is allergic to penicillin and that Jeff was a multimillionaire widower with a step-daughter named Patricia and a former cook for the band Blues Traveler and owned the rights to their first album. However, he gave the rights to his step-daughter as a fiftieth birthday present.
- In "Portrait of Francine's Genitals", Jeff reveals that he has taken Hayley's last name after their marriage, making him Jeff Smith.
- "Pilot (American Dad!)"
- "Stan Knows Best"
- "Francine's Flashback"
- "Roger Codger"
- "Bullocks To Stan"
- "Stan of Arabia: Part 1"
- "It's Good to Be the Queen"
- "Dungeons and Wagons"
- "Bush Comes to Dinner"
- "A.T. The Abusive Terrestrial"
- "Joint Custody"
- "The Vacation Goo"
- "Pulling Double Booty"
- "Phantom of the Telethon"
- "Shallow Vows"
- "Bully for Steve"
- "100 A.D."
- "Son of Stan"
- "There Will Be Bad Blood"
- "The People vs. Martin Sugar"
- "For Whom the Sleigh Bell Tolls"
- "I Am the Walrus"
- "License to Till"
- "Jenny Fromdabloc"
- "Home Wrecker"
- "The Worst Stan"
- "Season's Beatings"
- "The Unbrave One"
- "Stanny Tendergrass"
- "Dr. Klaustus"
- "Less Money, Mo' Problems"
- "Stan's Best Friend"
- "The Kidney Stays in the Picture"
- "Toy Whorey"
- "Love, American Dad Style"
- "Killer Vacation"
- "American Stepdad"
- "Why Can't We Be Friends?"
- "Adventures in Hayleysitting"
- "National Treasure 4: Baby Franny: She's Doing Well: The Hole Story"
- "Finger Lenting Good"
- "Naked to the Limit, One More Time"
- "Spelling Bee My Baby" (slideshow)
- "Lost in Space"
- "Kung Pao Turkey" (photographs)
- "Faking Bad" (mentioned)
- "Honey, I'm Homeland" (flashback)
- "The Longest Distance Relationship"
- "My Affair Lady" (mentioned)
- "Holy Shit, Jeff's Back!"
- "Seizures Suit Stanny"
- "Hayley Smith, Seal Team Six"
- "Stan Smith as Keanu Reeves as Stanny Utah in Point Breakers"
- "Kiss Kiss, Cam Cam"
- "The Devil Wears a Lapel Pin"
- "Stan-Dan Deliver"
- "The Two Hundred"
- "The Dentist's Wife"
- "Daesong Heavy Industries"
- "Daesong Heavy Industries II: Return to Innocence"
- "Criss-Cross Applesauce: The Ballad Of Billy Jesusworth"
- "Garfield and Friends"
- "Gifted Me Liberty"
- "Fight and Flight"
- "The Enlightenment of Ragi-Baba"
- "Portrait of Francine's Genitals"
- "Bahama Mama"
- "Roger's Baby"
- "Ninety North, Zero West"
- "Whole Slotta Love"
- "Bazooka Steve"
- "Camp Campawanda"
- "Julia Rogerts"