Transcript for A Final Farewell to 'American Idol'
The show "American idol" made TV history, launching careers and for a while scoring huge ratings. Put in the brutal world of primetime, few things last forever. ABC's David Wright on "Idol's" farewell show. This is "American idol"! Reporter: 15 seasons, 555 contestants -- âª Reporter: 11 judges, and tonight, "American idol" sings its swan song. Mega stars, past winners, and former judges gathered one last time for the finale. Even the president sang its praises. It inspired young artists and captivated audiences across the country. And it taught America what it means to be pitchy. Reporter: Former judge Jennifer Lopez capitalizing on all the attention -- âª I ain't your mama âª Reporter: To debut her own song. That's why she's an "American idol," folks. Celebrating a show that's changed TV and music both. âª Reporter: "American idol" was interactive, empowering viewers to pick the next big star, giving contestants a truly national audition. I think that was really exciting for people to do and to watch together with other people and to see their person make it. Reporter: People watched because you never knew if that next contestant might just be the next big thing. It was like this giant Cinderella story are everybody knew Kelly Clarkson had been a waitress. The winner is Kelly Clarkson! Reporter: Kelly Clarkson was an unknown singer from Texas when she won seen one of "American idol." TV moment that seemed to last a lifetime. Today she's a bona fide star. She's sold nearly 18 million albums with hits like "Stronger" and "Since you've been gone." From the start I thought Kelly Clarkson was a great sing letter are she's a very strong person. And that really came through in the career that she's had ever since. Reporter: Even "American idol's" losers could end up being dream girls. Like Jennifer Hudson, sent home early on season three, despite being widely praised by the judges. But it all worked out in the end for Hudson. âª Jennifer Hudson! Reporter: That performance won her an Oscar. She may not be an idol. But there's no better consolation prize. Who doesn't love Carrie Underwood taking a smoke break. âª Sometimes I need a smoke break âª Reporter: Mostly belting out powerhouse anthems like "Before he cheats." âª Before he cheats âª Reporter: 11 years ago she was just another contestant on season four. âª Cause I can't make you love me âª Going to L.A. For me for "American idol" was so scary. I was crying like in the car on the way to the airport. Not only was I flying for the first time, I was flying by myself. Reporter: Simon Cowell knew talent when he heard it. I will make the prediction, not only will you win this show, you will sell more records than any other previous "Idol" winner. Reporter: He was right. Carrie Underwood has gone on to sell more than 58 million albums and win 13 grammys. I love that she's gone on to be a big star and he had predicted that, Simon. Reporter: Cowell's signature snarkiness was a trademark. Amazingly dreadful. Reporter: Chemistry part of the early success. I will bow to the god of Paula Abdullah. Reporter: Paula Abdullah got a spinoff reality show "Hey Paula." The star's odd behavior led some viewers to question whether she had a substance abuse problem. I am exhausted! Reporter: Allegations she addressed on "Nightline" in 2009. I've never been addicted to any prescription drugs. I've never been drunk. I have worked my whole life. I'm not the girl that's in those tapes. Reporter: Paula, Simon, and randy eventually moved on themselves replaced by a revolving door of celebrities. Among them Ellen degeneris, Steven Tyler, Jennifer Lopez, and of course Nicki Minaj who feuded with cojudge Mariah Carey. Nobody said every moment, excuse me, that the -- can I make -- oh, doorling -- It was really fun to watch because they really are two divas. Their feuds were all about themselves. This is "American idol"! Reporter: The one constant on the show, perennial host Ryan Seacrest. I was terrified. I put on a brave face the first couple of episodes. I wasn't quite sure how to run a live television show. Reporter: In 15 seasons there were plenty of diamonds in the rough. âª Hit me when the wind blows âª âª Reporter: Some just plain rough. âª Talk to me tell me your sign âª Reporter: Remember William hung? And his rendition of "She bangs" one of the many unforgettable performances on "American idol." âª Looking like a fool with your pants on the ground âª Reporter: If imitation is the greatest form of flattery "Idol" must have been beloved, paving the way for shows like "America's got talent," "X factor," "The voice." "The voice" was a little copycat version of "American idol," really. I don't think it's really about who wins it because -- I mean, I've watched it enough, I don't even know anybody from it. Reporter: Viewership declined as fresh talent turned to social media. Bypassing the TV middleman altogether. Justin Bieber was discovered on youtube. Shawn Mendes was discovered on vine. The winner of "American idol" season 15 is -- Reporter: All good things Harvin! Reporter: So tonight, one final bow. I'm David Wright for "Nightline"
This transcript has been automatically generated and may not be 100% accurate.