Still, she averages just one starring episode per season (which is at least more than Marge earns), in favor of further episodes of Bart’s and Homer’s endless antics. After all these years, most of the characters have fallen into the inevitable rut of recycling their greatest hits, essentially becoming cartoons of themselves (yeah, but still…): Homer is a dumb, slothful, glutton who finds new ways of injuring himself each week; Bart is ever the irredeemable imp, always wreaking havoc, getting his comeuppance, wreaking further havoc; and Marge remains the suffering but simple mom and wife, cleaning after and caring for her incorrigible family.

But Lisa--she yearns for something more. She wants to better herself, her family, her town. We’ve seen Lisa happy and sad, we’ve seen her fall in love and be scorned, we’ve seen her struggle for recognition, strive for acceptance, threatened by rivalry, and saddened by failure. Her brother has betrayed her, her father has failed her, her grandmother deserted her. Lisa is actually a three-dimensional character with complex emotions, alone among the one-note caricatures on the show.

Sure, she’s a nerd--who among Simpsons fans isn’t? She’s also a Buddhist, a vegetarian, an environmentalist, an extreme leftist, and from all appearances, a chronic depressive. Luckily she channels this into creativity—poetry and plays and, of course, the sax. She’s sensitive to a fault, and cannot lie. She stands by her convictions to honesty and truth above all: she will not watch Homer’s stolen cable television; she berates Congress after witnessing a bribe in action. She brought down Whacking Day, stood up against sexist Malibu Stacy dolls, rallies against Laramie Cigarettes, and fights for causes she knows can’t win. Lisa even exposes the hypocrisy of the liberal Fox network vs. the rightwing Fox News!

Not just an overachieving genius and hopeless do-gooder, she’s also frequently the voice of the reason. When all of Springfield believes in aliens or angels, Lisa is the one to quell their hysteria. And when there’s a mystery afoot (like the nefarious "Who Shot Mr. Burns?" cliffhanger), Lisa will solve it.

It’s no coincidence that there is exactly one character who is smart and good in a show populated by morons and lunatics; The Simpsons is notoriously written by an army of Harvard grads … the smart, leftwing voice of reason? Yes, that is clearly their voice.

But Lisa is also, let’s not forget, a little girl—she loves ponies and dolls and frequently falls victim to hopeless puppy-love crushes. Because poor little Lisa is the only character with a heart, hers is destined to be broken. In some of her earliest starring episodes, she had an unrequited crush on substitute teacher Dustin Hoffman … er, Mr. Bergstrom, who left her with the inspiring words “You are Lisa Simpson” before sailing off into the sunset; her musical hero, Bleeding Gums Murphy, is now playing his bloody sax at the great gig in the sky. That hippie activist voiced by Pacey from Dawson’s Creek turned out to be a loony eco-terrorist. Her fling with the bully Nelson ended with Nelson being, well, Nelson. Her paternal grandmother, a radical fugitive with the voice of Glenn Close, showed Lisa that smartness did indeed flow in the Simpson gene … and then deserted her, going underground once more (and a few seasons later, kicking the bucket). Even in alternate futures and a handful of hypothetical Halloween fables, Lisa’s heart is perpetually crushed and her dreams disappointed.

Lil' Lisa was the only person to ever redeem Mr. Burns’s black little heart, even if he predictably betrayed her in the end: when he went bankrupt, she taught him to recycle, which he did until he figured out how to market sea slurry with Lisa’s name and face on the package. When Mr. Burns offered her the 10% she deserved, Lisa had the stones to tear up that check, an act which gave Homer four heart attacks.

But what’s best about Lisa is that, though she’s smarter than her dysfunctional family, embarrassed by their antics, and beleaguered by their incompetence, she sticks with them no matter what. The whole family, for that matter, sticks together, through thick and thin. On the run from hillbillies or tricked by carnies or expelled from Australia or Brazil or England or France (that list keeps mounting…), the Simpson clan functions best as a team.

She has a typical brother-sister rivalry with Bart: he tortures her, she cries. But for all their antagonism, they’re accomplices more often than not, because though he wouldn’t admit it, Bart needs Lisa’s brains, and Lisa needs a little bit of fun that only Bart could provide. (He also defends his lil’ sis from bullies and bears with regular frequency.) Bart and Lisa are at their best when they’re causing high jinks together: fleeing Sideshow Bob or rescuing Krusty’s career or bailing Homer out of whatever ridiculous predicament he’s gotten himself into this week … Bart and Lisa’s friendship provides some of the most touching moments on the show.

Back in 1990, President George H.W. Bush famously slammed our favorite family, citing them as the model of dysfunction. What he of course failed to see was that there is actual warmth to these little yellow oddballs! Homer and Bart are usually her antagonists, but it’s the love of her father and brother that keeps Lisa from becoming the bitter, dejected outcast--say, Meg from The Family Guy. In Lisa’s future episode, during her impending wedding to Hugh, the snobby Brit, he tries to yank her away from her family and hometown. “You’re better than this place; you’re like a flower that grew out of a pot of dirt,” he tells her. When she protests, he reasons that she complains about her family more than anyone. “Maybe,” she answers, “but I still love them!” And that’s why Lisa wins.

Bart and Homer are the crowd-pleasers, no arguing that: their misadventures dominate the show, and their faces hog the merchandise. Otto or Disco Stu or Comic Book Guy might be the fan favorites. But it's Lisa, the second-grader reading at a 14th-grade level, who is the heart and soul of both the family and show.