Editor’s Note: Watch “TV on the Edge: Moments That Shaped Our Culture” tonight, Sunday, at 9 p.m. ET on CNN. The four-part series runs through October 13.

For months before the 1997 premiere of “The Puppy Episode,” the groundbreaking episode of Ellen DeGeneres’ hit sitcom “Ellen,” rumors swirled that the comedian and her fictional counterpart would come out as gay.

Anticipation ballooned as the air date approached. An early script for the episode was leaked. The comedian teased the reveal in interviews. DeGeneres herself came out on the cover of Time a few weeks before the episode premiered. So when it was finally time for “The Puppy Episode” to air, audiences could hardly stand to wait a second longer for the character of Ellen Morgan to say those two words.

And still, they had to wait. At the top of the episode, Ellen’s friends grow impatient with her as they wait for her to exit the bathroom.

“Ellen, are you coming out or not?”

“Yeah, quit jerking us around and come out already!”

Ellen pokes her head out from behind a door as her friends grow impatient.

“What is the big deal, I’ve got a whole hour!” she quips.

It’s a joke-dense, hour-long episode of “Ellen,” rife with meta nods to Ellen’s sexuality. Until “The Puppy Episode,” the character had rarely dated and mostly resisted romance, deviating from sitcom conventions of the time and frustrating network executives. The episode’s title apparently came from a comment former Disney CEO Michael Eisner made after suggesting that, if Ellen wouldn’t go on dates with men, then maybe she could, at the very least, adopt a puppy.

Ellen Morgan never did get that puppy, but the episode made history as Ellen became one of the first out gay lead characters on TV. Though “Ellen” was canceled after five seasons, “The Puppy Episode” endures. Its influence has been analyzed by academics in dozens of articles since its premiere, and it opened the door for future successful sitcoms, like “Will & Grace” and “Modern Family,” to feature gay leads.

Dava Savel, co-showrunner of “Ellen’s” fourth season, has written dozens of episodes of TV in her long career. She’s still chasing the “lightning in a bottle” she found in “The Puppy Episode.”

“I think the episode really just touched a very sensitive button in this country,” she told CNN. “That’s why it worked — because it was real.”

How ‘The Puppy Episode’ got made

The making of “The Puppy Episode” started with DeGeneres.

The comedian invited the writers to dinner ahead of the fourth season and announced that she wanted her character, Ellen Morgan, to come out as gay. (Her coworkers knew DeGeneres was gay, though she hadn’t yet come out on the national stage.)

“It all started from her, wanting to be true to herself,” Savel said. “Imagine not being able to be who you really are — ‘my character’s this way, but I’m this way.’ Oftentimes, the characters, they meld into the person who’s played them and vice versa.”

After getting the go-ahead from Disney TV executive Dean Valentine, Savel and her three co-writers on the episode got to work, interviewing gay “Ellen” writers and cast members about their own coming-out experiences. It was a gamble, but one they were excited to take on as they mapped out the season and its path toward Ellen’s admission.

“This was an established character on a big show — one of the biggest shows they had — and either it was gonna work, or it was gonna kill it,” she said.

The writers had some requests for ABC: It had to be an hour long, and it had to air after “sweeps week,” the period when networks set advertising rates for their series based on viewership. Episodes that air during sweeps were known for staging publicity stunts to attract larger-than-average ratings — Ellen’s coming out couldn’t come off as “gratuitous,” Savel said.

For the moment to feel earned, writers laid breadcrumbs all season long until Ellen finally confronted her sexuality. Gay innuendos abound from the first episode of Season 4: A microwave or doorbell dings when a character says the word “gay,” Savel said. In one scene, Ellen sings “I Feel Pretty” from “West Side Story,” pausing just before she reaches the “gay” lyric. And all season long, Ellen visits a series of shrinks who probe why she feels so insecure and unhappy, though she keeps coming up empty.

It takes meeting Susan, an out gay woman played by guest star Laura Dern, for Ellen to finally feel comfortable coming out. The two have instant chemistry after meeting early in the episode. After admitting to her latest therapist — this time, played by none other than Oprah — that she has feelings for Susan, Ellen rushes to the airport to see her love interest again, finally comfortable expressing something she’s never been able to say.

“I can’t even say the word,” Ellen says in the episode’s pivotal scene, visibly frustrated with her inability to voice her feelings. “Why can’t I say the word? … What is wrong, why do I have to be so ashamed? I’m 35 years old. I’m so afraid to tell people.”

And then finally, inadvertently delivered into a microphone at an airport gate, she gets there: “Susan, I’m gay.”

Fans applauded ‘The Puppy Episode’

More than 42 million people watched the episode live, a significant surge in viewership from the rest of the season.

The episode generated the expected backlash — “letters, death threats,” said Savel; and an ABC affiliate in Alabama refused to air the episode — but the hate was drowned out by heaps of letters from gracious fans who said the episode gave them the courage to come out, too.

Savel saw the impact firsthand. After she won an Emmy for co-writing “The Puppy Episode” in 1997, she headed backstage with her fellow writers and DeGeneres to meet the press. But on their way there, they were met with lines of caterers and servers working the event, pausing their work to applaud and congratulate the group from “Ellen.” It still makes Savel weepy, she said.

“We were soaring,” Savel said. “Those moments of truth — that’s what it was all about.”

Rachel Loewen Walker, an assistant professor in women’s and gender studies at the University of Saskatchewan in Canada, still shows “The Puppy Episode” to her students, many of whom didn’t know DeGeneres once starred in a sitcom.

“(The episode) was such a pivotal moment in queer representation on screen especially because of its context: The much-loved Ellen Degeneres was actually gay,” Loewen Walker told CNN. ”Her coming out made it so much more than an onscreen story. It made it real in a way that sitcoms often aren’t allowed to participate in the everyday.”

‘Ellen’ ended after the character came out

Savel and other writers were fired after the fourth season, she said, as “Ellen” entered a new phase. The fifth season starred a newly confident Ellen as she went on dates, found a serious girlfriend and enjoyed her life as an out gay woman. (Throughout the season, ABC slapped parental advisories onto episodes that featured gay content, against DeGeneres’ wishes.) The “new” Ellen was a huge shift from the self-effacing protagonist who actively avoided romance earlier in the series.

Ratings for the new season tanked, and “Ellen” was canceled in 1998. (ABC never said as much, but Loewen Walker and others who’ve studied the series’ impact have surmised that the show was “too gay” for the network at the time.)

DeGeneres returned to TV in 2001, playing another gay character in a short-lived CBS sitcom called “The Ellen Show.” She wouldn’t play a fictional version of herself again, instead launching a successful daytime talk show in 2003.

“Looking back on ‘Ellen,’ I feel as though (DeGeneres) shouldered such a huge burden back then, for so many future queer characters,” Loewen Walker said. “It feels like that absence meant that many others were able to have presence.”

‘Ellen’ changed TV, but representation has a ways to go

“The Puppy Episode” did something that’s still unusual in TV — it took a beloved character, developed with care over several seasons, and upended her fictional life. Ellen Morgan grew from the bumbling, charming “girl next door,” as the character was frequently described by network execs, to a self-assured, charismatic gay woman who makes no apologies.

Even a year later, “Ellen’s” influence was apparent. When “Will & Grace” premiered a year after “The Puppy Episode,” protagonist Will and his flamboyant friend Jack didn’t have to come out like Ellen did — the characters were introduced as gay in the pilot. Over a decade later, the couple Mitchell and Cameron and their adopted daughter, Lily, charmed audiences as key members of “Modern Family’s” Emmy-nominated ensemble. Now, there are series built entirely around young queer characters, like the teen series “Heartstopper,” a Netflix mega-hit.

Lesbian representation on TV, though, has made somewhat smaller strides since “Ellen,” Loewen Walker said. Characters like Arizona Robbins on “Grey’s Anatomy” and many of the women of “Orange Is the New Black” were out lesbians from the moment they were introduced, and series like “The L Word” starred a cast of almost exclusively lesbian characters. But those characters were often subjected to violence and tragedy or, in the case of the original run of “The L Word,” were criticized for falling into stereotypes or offensive misconceptions of lesbians.

“It’s still rare to see lesbians in that primetime, cable television sitcom spot,” Loewen Walker said. “‘Modern Family’ really brought two gay men into our homes, but I can’t think of a lesbian or queer woman that has attained the same family-friendly welcome.”

DeGeneres did receive that welcome, though, as a talk show host beloved by millions of viewers for celebrity pranks and generous gifts to everyday people. Much of that goodwill was lost when reports accused her of running a toxic workplace. (DeGeneres addressed the hit to her reputation, with mixed results, in a recent Netflix stand-up special she said would be her last.)

Savel hasn’t worked with her since 1997, though she remembers DeGeneres being a “tough,” exacting boss with the “goods to show for it.” But “The Puppy Episode” will always be a part of DeGeneres’ legacy.

“She is still forever frozen in this episode as a champion of people — oppressed gay people in the closet,” Savel said. “You can say you got an Emmy and a Peabody. It’s more than that. You have an entire country that remembers when this happened.”