Nearly every character in Family Guy has gone through dramatic changes.
- Perhaps the most radical is Stewie. Once an egomaniacal baby genius, bent on world domination and matricide, Stewie has evolved into an effeminate, gay infant with a penchant for occasionally whipping out some manner of advanced technology.
- In "If I'm Dyin', I'm Lyin'", Peter's blasphemous actions result in modified versions of the plagues of Egypt descending on Quahog. It is Brian who realizes the significance of the biblical events and when Peter insists "there must be a logical explanation" Brian slaps him repeatedly and states "Here's an explanation,*slap* GOD *slap* IS *slap* PISSED!". Evidently dogs don't have the best memory because Brian later became an outspoken hard line atheist an entire season AFTER Jesus became a tenant in the Griffin house.
- In Mayor West's first two appearances, he appears to be more of a Bunny-Ears Lawyer compared to the rest of the series. He's first introduced telling the story of the city's founding, and the humor is coming entirely from the ridiculousness of the (apparently completely true) story. On his second appearance, when he meets Peter Griffin, he is actually helpful until he discovers that Peter's property is not part of the United States. Then though, he reveals the trapdoor in his office (and his plans for further work on it), and his characterization is set.
- Likewise, Glenn Quagmire was initially portrayed as more of a '50s-type swinger fellow and seems quite normal in comparison to the extreme pervert he would eventually become; he was also very unsuccessful at attracting women before becoming the sort of guy who beds a different woman every night (often by immoral and illegal ways, such as roofies, an elaborate mechanism in his couch that sprays any woman who sits on it with knock-out gas, strips her clothes, and spreads her legs and lies her on her back while disco music plays [as seen and demonstrated in "It Takes a Village Idiot and I Married One"], and emotional manipulation). And even later than that, Quagmire still kept his near-rapist ways, but was shown to hate Brian with a passion (compare with some early episodes where Quagmire and Brian, despite not interacting much, were on friendly terms), and actually care about two women in his life: his sister, who's being abused by her boyfriend, and Cheryl Tiegs, the one woman he loved so much, that he became a sex addict when she broke up with him.
- Quagmire's vendetta with Brian was also quickly altered in the course of only two seasons. Starting with "Jerome Is the New Black", a Running Gag began with Brian trying to kiss up to Quagmire only to accidentally offend him into a rant-inducing slight; as episodes passed, Brian began to make subtle retorts back at Quagmire, who became increasingly vindictive and lashed at Brian more gratuitously. This reached the boiling point in "Tiegs For Two" where both are Sitcom Arch Nemesises and Brian is even less capable of hiding his utter disgust and contempt for Quagmire and vice versa, and eventually starts a very personal Escalating War. Following this, the feud became Running Gagged and they converse with each other normally outside a handful of very subtle conflicts.
- It is odd to watch the early episodes where Meg was treated with respect and love by her family, like Peter trying his hardest to help her out at the school newspaper. Also, when Meg and Chris are both in front of an air fan, Meg complains that Chris is hogging all the air to which he replies "Yeah well, YOU'RE hogging all the UGLY!" Unlike the later barrage of "Meg is ugly" jokes, this is merely intended as a petty insult that would be uttered during a fight and likely not genuine.
- "Brian: Portrait of a Dog", Brian's first spotlight episode revolved around him being talked down to for being a dog. Lois chastises Peter for treating Brian this way and the family learn to treat Brian with dignity. Later episodes slowly make a Running Gag of the family manipulating or mocking Brian's forcive dog-like tendencies and at least once pointing he is semi human and disposable to them, usually with Lois herself being the most condescending and bullying towards him.
- The earlier episodes actually revolved around Peter and Lois' well intentioned attempts to raise and provide for their family and, while retaining selfish tendencies, often learned an Aesop from the episode's events. As the show progressed, they both gradually evolved into being exaggerated self centered Abusive Parents for laughs, making the show's title rather ironic (which was probably the intention all along, considering that Family Guy is often regarded as either an anti-Brady Bunch or The Simpsons if it knew how to do Comedic Sociopathy without pissing off its viewers).
- In Joe's first appearance in "A Hero Sits Next Door", Meg hit on his son. He was slow to respond, but that was because she was so awkward. By the end of the episode, he seemed to genuinely enjoy her company. She also had a couple other boyfriends in the past. Compare to present day when boys will do anything to stay away from her, like commit suicide or murder a sibling so they can be too busy with an upcoming funeral.
- In the earlier episodes, Joe was a mild mannered wheelchair bound cop who is generally friendly towards everyone and well respected because he's crippled but capable. Later episodes have him constantly abused by Peter and other people due to being crippled, he has a severe anger problem often lashing out at and beating up his friends, and sometimes depicted as being depressed.
- Also, in their first appearances, news reporters Tom Tucker and Diane Simmons were just two news anchors who may or may not have been attracted to each other, but the viewer wouldn't know, since their main schtick was being politically incorrect while delivering the news (like when Tom declared himself Jesus Christ or Diane mentioning a "freak heat wave" and Tom telling her that it was offensive towards his upside-down faced child). Through most of the show's run afterward, they dislike each other and constantly take shots at each other about how unattractive the other is.
