Bartholomew "Bart" Simpson is voiced by Nancy Cartwright (that's right, a woman!) and is Homer and Marge's only son on The Simpsons.  Bart is an underachiever and was definitely much more of a bad boy in th ebeginning seasons of the show.

Now, Bart, although he has not aged, has certainly matured as a character.  Do the Bartman people.

Bart Simpson Quotes

Lisa's Brain: Poor predictable Bart. Always takes 'rock'.
Bart's Brain: Good ol' 'rock'. Nuthin' beats that!
Bart: Rock!
Lisa: Paper.
Bart: D'oh!

Bart: Take him away, boys.
Chief Wiggum: Hey, I'm the chief here! Bake him away, toys.
Lou: What'd you say, chief?
Chief Wiggum: Do what the kid said.

The Simpsons Quotes

The Constitution? I'm pretty sure the Patriot Act killed it to ensure our freedoms.

Bart

Homer: (Wearing glasses) The sum of the square roots of any two sides of an isosceles triangle is equal to the square root of the remaining side!
Man: (From inside a bathroom stall.) That's a right triangle, you idiot!
Homer: D'oh!