Stewart Gilligan "Stewie" Griffin, voiced by Seth MacFarlane, is a fictional character in animated television series Family Guy. With machiavellian tendencies and a wicked British accent, the toddler regularly plotted the demise of his doting mother Lois early in the series, and gradually underwent a change in character from "a Bond villain to a closet homosexual," says creator Seth McFarlane on the DVD Commentary track for the episode "Fifteen Minutes of Shame".

Stewie's nose is drawn as a forward-pointing triangle, like that of his mother and sister. This is unusual, because very rarely are other males drawn with such noses. Also unusual is Stewie's football-shaped head. An explanation is given for this in a flashback. Brian was babysitting him (he had a normal head at this point) and he was jumping on the bed. Brian tells him to stop at which point Stewie yells, "shut up, you aren't my mother!" and jumps especially high, promptly smashing his head into the ceiling and flattening it into the football shape. (This contradicts flashbacks to Stewie's birth, when he has a football-shaped head.) Stewie has remarked that he's just not a hat person ("When You Wish upon a Weinstein").

Stewie's voice and speech are very reminiscent of Doctor Zachary Smith from the 1960s television series Lost in Space, and that of British actor Rex Harrison, suggesting some degree of parody. In reality, the creator's comments toward the actor suggest that the voice was in fact chosen in tribute, sometimes called homage. Seth MacFarlane mentions that Stewie is based on Rex Harrison in the play My Fair Lady several times during the DVD commentary tracks of the series. Also, on The Late Show with David Letterman, Seth stated that Stewie is "Rex Harrison in a female's body."

This is further reinforced in the episode "One if by Clam, two if by Sea" where Stewie bets Brian he can train a Cockney girl to present herself as a lady (the basic plot of My Fair Lady), and in the episode "Running Mates" in which he sings the Rex Harrison song "I've Grown Accustomed To Her Face", also from My Fair Lady.

Despite his constant plotting, Stewie also shows affection for his mother, for instance when away visiting his grandparents. He also eventually began to show homosexual tendencies and has been caught cross-dressing, an event that was used successfully for blackmail by Brian. This character transition came about largely in Season 3.

So, Can the Family Understand the Baby, Or What?

Most episodes imply that no one understands Stewie's fast talking dialogue except for the family pet, Brian, leading to the humorous setting where everyone understands the talking dog while not understanding the child. In the DVD audio commentary for the episode "E Peterbus Unum", series creator Seth MacFarlane states that adults can understand Stewie but don't take him seriously, "sort of like...if a four-year-old who [can] talk told you to 'f___ off'."

In at least one episode, however, Lois shows signs that she understands his threats but dismisses them with a warning. It could be argued that Lois selectively understands Stewie. In the episode "Running Mates", when Stewie learns that Lois is running for public office, he exhorts Lois to get to work on it and lists things a candidate should be doing, such as "kissing babies". Lois then kisses Stewie, who complains, "Not this baby." In the episode "Brian in Love", Stewie keeps asking Lois for kisses in order to make Brian jealous, and Lois remarks that Stewie is feeling "very affectionate" that night.

Non-reoccuring adults often clearly understand the content of Stewie's talk. In the episode "Peter Peter Caviar Eater", while at Cherrywood, Stewie summons three servants, orders one to fetch him the Wall Street Journal and the remaining two to fight to the death, which they do. Later in the same episode, he has a discussion on foreign economics with three adult guests.

In the ending of the episode "E Peterbus Unum", there is a self-referential joke relating to the widespread confusion among fans surrounding this issue. The title of this section "So, Can the Family Understand the Baby, Or What?" is a direct quote from the scene, which takes place deep in the future in a history classroom.

Seth, however, has asserted that he and his staff will never take a definite stand on the issue, and that whether or not the other characters understand him will depend entirely on what joke the writers are doing at the time when the conversation takes place.