Maggie is the youngest of the three kids to Homer and Marge Simpson, and is the younger sister to Bart and Lisa. When Marge became pregnant with Maggie, Homer felt that we was finally financially secure, so he quit his job at the Nuclear Power Plant and took a job at the Bowling Ally, with only enough pay to support the family of four, with Maggie's arrival, Homer took his job back at the Nuclear Power Plant. But despite feeling depressed about having a third child, and working in a terrible job. Homer loved her all the same.

Maggie has shown to be a baby genius, following in her sisters steps and likely due to the absense of the Simpson Gene that effects Homer and Bart. She is able to recognise complex equations such as E=MC², she can write her own name, and can recognise colours, and most importantly, she is able to drive the family sadan. In FABF09 - Smart and Smarter, it is revealed that Maggie had an IQ of 167, surpassing even Lisa. But it was later revealed that Maggie was cheating with Lisa's aid, however, Maggie still proved her natural smarts by being able to play Lisa's sax rather well.

Given her age, Maggie is impressionable. She can be quite often seen mimicking various things she sees going on around her such as hitting Homer in the head with a mallet after watching Itchy and Scratchy and later, when the show becomes lame, she gives him a glass of lemonade.

Maggie has proven herself to be quite a remarkable marksman despite her age. With toy dart guns, she is able to accurately shoot pictures of Homer, and she also shot Mr. Burns with a revolver, though that was mearly a discharge. She also managed to save both her parents from an attack by Fat Tony and his gang with a Sniper Rifle.

Maggie does have an enemy in Gerald, the one eye-browed baby, though the two are only shown to fight when neither of their parents are looking as shown in LABF18 - Pranks and Greens, when both Maggie and Gerald are in the same room, and arent exchanging dirty looks with each other. Various issues of Simpsons Comics particularly Simpsons Comics #47 - The Rise and Fall of Bartholomew Simpson reveals that the two stop fighting later in life and get married, though Gerald interupting Maggie does annoy her.

Maggie has proven herself to be quite a hero. She has saved her family numerous times sometimes without them even knowing. Such as when she caught a beer bottle that was headed right for Homer's head and the previously mentioned shootings. She saved Homer and Bart in The Simpsons Movie from Russ Cargill who was brandishing a shotgun at them, Maggie showed up and knocked him out with a rock, showing that she probably has some pretty strong arms.