When "30 Rock" premiered in the fall of 2006, it was expected to be crushed by NBC's other new series, also set behind the scenes of a late-night sketch comedy show, Aaron Sorkin's heavily hyped "Studio 60 on the Sunset Strip."

"The first year, our biggest concern was that we thought that NBC had this very clear imperative to choose between us and 'Studio 60,' " recalls Alec Baldwin, who plays slick corporate executive Jack Donaghy on the sitcom, which is in its final, 13-episode season. "We were all very convinced we were going to be the losers there."

Of course, they weren't. Six years after its touch-and-go freshman season, "30 Rock" has attained a curious place in television as a perennial underdog and a critical darling. Its ratings are a fraction of broader sitcoms like CBS's "Two and a Half Men" and "The Big Bang Theory" -- last season "30 Rock" averaged about 4.7 million viewers, while "Big Bang" drew nearly 15.7 million in a recent weekly Nielsen report -- and "30 Rock's" failure to find a larger audience has frequently been written into the show itself.

Meanwhile, "30 Rock" and its stars, Baldwin and series creator Tina Fey, have racked up dozens of nominations and awards from the Emmys, Golden Globes and Screen Actors Guild, and it is widely regarded as one of the finest sitcoms of the past 10 years. Although "30 Rock" has never quite attained the cultural ubiquity of a series like "Seinfeld," the show's imprint is evident across today's TV dial -- from the smart but flawed heroines of "Girls" and "The Mindy Project" to the postmodern, single-camera comedy of "Community" and "Don't Trust the B-- in Apartment 23."

"Our No. 1 goal when we started was to be allowed to finish it," executive producer Robert Carlock says.

The series opened at a dark time for sitcoms -- particularly at NBC, whose Thursday night "Must See" lineup had dominated the ratings for much of the previous decade. Two years after the series finale of "Friends," though, NBC had only three other sitcoms in its prime-time schedule (by comparison, the network now has 10, with more to come at midseason).

The "30 Rock" writers in early 2006 also were acutely aware of the cancellation of "Arrested Development," a sitcom whose profile was eerily similar to their own: critical buzz, a small but passionately devoted following, a cast full of oddball characters and a blistering jokes-per-minute rate.

In hindsight, the looming threat of annihilation may have been a boon to the show. "Creatively, we were eager to stuff as much as we could into every episode," Carlock explains. "And that may have lent some of the breakneck pace and tone of the show, that feeling of 'This could go away.' "

Fey and Carlock originally set out to make a live-action version of "The Simpsons," a goal that Carlock now describes as "idiotic and untenable from a production standpoint."

"We wanted to be comically ambitious and thematically ambitious. We wanted to do stories about gender politics and economic disparity and race, and make them funny," he says.

As for the show's unlikely survival, it certainly helped that "30 Rock" started piling up Emmys, winning for comedy series in its first three years (and earning a nomination every year it's been eligible). "30 Rock" also attracted young, upscale and highly educated viewers -- a demographic coveted by advertisers.

Baldwin also suspects that the show's popularity among the Hollywood executive class may have kept it alive. "They were running a show that people in the business thought was special," he says. "You walk into a room and someone who's the head of a network says, 'My son broke his leg skiing, and he was in bed for two weeks and we watched three seasons of your show on DVD.' "

Adds Carlock, "Both inside and outside the industry, among my friends, this show tops anything I've worked on in terms of people I know liking it and watching it."

Carlock, a veteran of "Friends" and "Saturday Night Live," can't explain why the series hasn't attained the stratospheric mainstream success of "Seinfeld" -- a show, in its own way, at least as eccentric as "30 Rock." "If I had the answer to that question I would have answered it," he says wearily.

What the show lacks in "Yadda, Yadda, Yadda" moments, it has made up for with its star, Fey.

She came to "30 Rock" from "Saturday Night Live," where she was the show's first female head writer and, as anchor of "Weekend Update," one of the most prominent female performers in its history. "30 Rock" made her a bona fide star.

"I think the real legacy is Tina as a writer, female or otherwise," Baldwin says. "She can probably go on to be the next Nora Ephron or Nancy Meyers. Her options are limitless, and I think people will look at this as the next step in her career."

For the time being, though, Fey is staying in the TV business. She recently signed a four-year development deal with Universal Television, the studio behind "30 Rock." There's little doubt she's made the medium a safer place for other whip-smart, funny women such as Mindy Kaling, Lena Dunham, Amy Poehler and "New Girl" creator Liz Meriwether.

Baldwin also has seen his career take an unexpected turn at "30 Rock." Television was once seen as a demotion for fading movie stars; Baldwin has proved it can be a viable -- even desirable -- career choice.

He's also created a new kind of comic hero in the form of Reagan-worshiping, free-market champion Jack Donaghy, boss and unofficial life coach to Fey's chronically disheveled Liz Lemon.

"The character has definitely crept up on me inch by inch over the years," he says. "If I see someone wearing the wrong colored tie with their suit, I'm disturbed by that. If a waiter interrupts my conversation with some hideous question, I'm appalled by that. So I think Jack Donaghy will be with me to my last days."

Baldwin is wistful about the end of "30 Rock." "We all realize as we leave that we'll probably never have another job like this again."

'30 rock'

When: 8 p.m. Thursdays
Where: NBC