College buddies Trey Parker and Matt Stone needed a theme song for their upcoming TV show, an irreverent cartoon about four foul-mouthed young boys in a Colorado mountain town called South Park.

When they asked avant-garde rock band Primus to record the intro music, not even bassist and vocalist Les Claypool thought they had a chance of making it to air.

"We thought 'The Spirit of Christmas' (the short films that laid the foundation of 'South Park') was very cool," Claypool said. "But we never thought it was gonna get on television, let alone become a worldwide phenomenon."

A quarter century after the series' 1997 debut episode, "Cartman Gets an Anal Probe," the Comedy Central series is still cranking out profane and often timely episodes, with recent shows dealing with Russia's invasion of Ukraine ("Back to the Cold War") and gentrification ("City People").

To celebrate the series' 25th birthday, Parker and Stone came full circle with a recent concert filmed at Red Rocks Park and Amphitheatre near Denver, headlined by Primus and alternative rockers Ween. The concert, which debuted on Comedy Central and streaming service Paramount+ on Aug. 13 and 14, respectively, featured musical numbers from the series' history.

"It's a wonderful thing to see these guys — who we never thought they would ever get on television — come in and basically change the world of comedy," Claypool said. "To still exist after 25 years is a major accomplishment. But to still be relevant after 25 years? That's epic."

The entertainment industry's streaming revolution and subsequent obsession with locking down well-known brands has proved highly lucrative for Parker and Stone. In 2019, the pair sold the "South Park" U.S. streaming rights to HBO Max in a deal valued at roughly $500 million. Last year, ViacomCBS — now Paramount Global — inked a $900 million deal for Parker and Stone to continue the series through 2027 and create 14 new hourlong TV movies for Paramount+. Full "South Park" streaming rights go back to Paramount by 2025.

This interview has been edited for length and clarity.

Q: How are you keeping the series fresh after 25 years?

Parker: We'll sit there in the writers' room sometimes and just be so stuck, and I'll be like, "How can we not know what the (expletive) we're doing after 25 years?" We never want to repeat ourselves. There's definitely tropes, but for it to be funny, it's got to be new. Just going, "Cartman is fat, and he likes cheesy poofs" is not going to make us laugh.

Q: Do the hourlong specials help open you up creatively?

Stone: I think it cuts both ways. I really like the "Pandemic Special" and the "Vaccination Special" Like a lot of people, we had to go fully remote, so we had to come up with a new production process, and that was pretty painful. The longer ones are sometimes really satisfying because Trey gets to write stuff that breathes a little more.

But then, we just went back to do our first series of six regular 22-minute shows after the pandemic, and I thought they were really great. It's almost like going back to our roots. It's like a pop song that's gotta be three minutes. These last hourlong specials we did were hard. We had a hard time finding our groove.

Parker: After we had done some specials and we went back to the regular season, it was definitely like, "Holy (expletive)." They felt so fast. And it felt like, "Dude, we've already got 15 minutes but we've got to finish this story." It was nice to go back to that, but it was also definitely jarring.

Q: "South Park" is often very topical, but you've always said your favorite episodes were the ones with the kids just being kids. How do you balance that?

Parker: It's easier to be fresh about something topical because it's new. The writers' room always starts with us sitting around a table going, "All right, what's going on?" Just like in any office. But even in the season we just did, some of my favorite things were Butters riding a horse and Cartman living in a hot dog. Just kid stuff.

Q: What was the closest you ever got to losing the show?

Parker: It was the same as everyone. It was the first few months of the pandemic, and it was the first time we were going "Oh, wow, maybe that's just it." Matt was the first one to say, "This thing's gonna go on a long time. Let's just start figuring out how to do it from home."

Not a lot of people know that we were a day away from starting production on the first feature movie we had done since "Team America: World Police." We were going to start shooting on the day that the pandemic shut everything down. It was months and months of getting ready for that movie, to just being like, "Nope, it's over."

I went to the office to start packing up my things because I was just kind of in shock. There was a few weeks of just depression, and then I just got happy 'cause I'm like, "I'm just gonna hang out with my daughter and watch 'Harry Potter' and build Legos." And then Matt said, "Let's go remote."

Stone: We always come back to "South Park." It's always there for us. We definitely want to go do other (expletive) in life, whether it's creative or just travel or whatever. We always want to do a movie, but movies are so hard to get going. We did Broadway, and that was an amazing experience. But then you come back, and there's those four boys, and it's like we don't have to go into startup mode.