Factual information:
Bart Simpson is the creation of Matt Groening. He is the eldest son of similar creations, Marge and Homer Simpson. He appears regularly on the animated TV show, The Simpsons, and, for some reason, in Butterfinger commercials.
He is voiced by Nancy Cartwright.
Analysis:
Bart Simpson, as a character, has gone through three distinct phases during The Simpsons' run: His initial conception was that of a simple bad-boy, who served merely as a figure in quaint, moralistic tales. A shadow of Dennis the Menace, with modernized slang and new catch phrases, to be sure, but nothing beyond. Eventually, though, Bart changed, his image as a trouble maker continued, but less in the manner of Dennis, in more in the Shakespearian fashion: Bart became a reborn Robin Goodfellow. A Puck. The last shift occurred when Bart suddenly found himself upstaged by his father, Homer. No longer the star of the show, Bart became a paradoxically self aware entity: Bart knew who he was, what part he played in American pop culture, but at the same time, remained static, and stagnated, unable to break the bonds of his image.
Bart's first incarnation is best seen as someone whom we may consider but a prototype at this point. In the early episodes of The Simpsons, Bart, (rather, the whole cartoon) was poorly drawn and shakily animated. Fitting with this simple appearance, the stories themselves were of equal depth. These show were primarily ethical/moral lessons. Remember when Bart stole the head of the statue of Jebediah Springfield? He felt guilty and brought it back. And, aww, he learned a lesson about tradition and culture in the mean time. Cute. Like when how he defends Lisa from the bully or when he learns the true meaning of friendship over a comic book.
I dunno, Davy....But if the series had kept up like this, it wouldn't have lasted. What's worse, is that about this time, The Simpsons were reaching a new height in popularity. If you quantify popularity by measuring the amount of crappy merchandise, that is. Bart's catch phrases "Eat my shorts," "Don't have a cow, man," and "Ay Caramba!" became tired and over used. A change was due.
The change was slight, but effective. Sometime around, say, season four or so, Bart became a little less cute...and a little more devious. Bart would be both the catalyst and the solution to the conflicts of the episodes. Indeed, Bart became more of a Puck and less of a...umm... boring Dennis the Menace rip off. Consider: The episode where Bart promotes the teacher's strike ("Purple monkey dishwasher!") with a little sly manipulation, and solves it, in a somewhat more blunt fashion. During this period Bart tends to have little adventures. He brings Krusty back together with his father, he foils Sideshow Bob's evil plans, etc.
This was a good period for The Simpsons, the shows tended to have wonderfully satirical writing, poking fun at most everything. At the same time, the show didn't take itself too seriously, it was willing to admit it's past ("Moooom!! She's using my catch phrases!" "Hush, you haven't used them in three years anyway!", Bart appears with a Dennis the Menace like slingshot in his back pocket in one episode, etc.), and move onward in more clever directions. The flaw though, is obvious. Similar to A Midsummer Night's Dream, each episode began and ended the same way; there was no change, no problem that went unsolved. Everything wrapped up nice and neatly.
Around the time they shot Mr. Burns things started to change again. Bart was no longer the headliner of the show, instead, probably for the better, Homer took the helm. Bart was reduced to the role of sidekick. He helps Homer collect grease as a money making scheme, he helps Homer gain weight to get on disability, he helps Homer grow tomaccos. Notice the lack of initiative on Bart's part? Though it's less glamorous, the sidekick role has served Bart well, it's allowed his character from becoming too overbearing, too overused. His former role as pop culture icon aides this ("Even I wouldn't do that, and I'm America's bad boy."). Bart's humor is preserved this way, without rotting or fading.
Due to his rather dynamic nature, I'm not sure how timeless Bart Simpson is as a character. He may just end up being a forgotten pop culture icon in years to come, but never the less, his popularity and influence need to be heeded in regards to the era.