No one knows what Jon Stewart's next move will be.

But when he crumples up his last script, tosses off his final riposte and leaves the Daily Show desk he's sat behind since January 1999, it won't be to join the ranks of the politicians he eviscerated.

"I understand that we're armchair quarterbacks. When are you going to be the head coach? I'm not as good at that. I'm really better at talking (expletive)," said Stewart back in November.

His impact, which Stewart is the first to downplay, has been immense. And since taking over for Craig Kilborn — Stewart's successor, Trevor Noah, takes over on Sept. 28 — Stewart has taken politicians to task, explained the arcane workings of Congress, vented against animal abuser Michael Vick, and shunned humor when moments of bloodshed, such as the church massacre in South Carolina, stunned the nation.

"He created something that did not exist," says late-night rival Jimmy Kimmel. "He made the show from a funny show to an important show. No one expected that to happen. Instead of a parody of the news, it became a critique of the news."

Here's how Stewart, a former struggling stand-up comedian with a short-lived 1993 MTV show under his belt, changed the face and tone of late night.

He was a late-night mentor. Stewart didn't shy away from sharing the spotlight. Like Saturday Night Live, which launched the careers of stars including Will Ferrell, Kristen Wiig and Adam Sandler, Stewart's set was a training camp of sorts for the big leagues. It gave us Steve Carell, Olivia Munn and John Oliver, among many others. "He provided a boot camp for talent," says former "Senior Black Correspondent" Larry Wilmore, now hosting Comedy Central's companion Nightly Show. "His legacy with other performers is huge."

He turned pundits and politicos into stars. Other late-night talk shows covet the A-listers to promote their various projects. Stewart, on the other hand, welcomed both established Hollywood stars like director J.J. Abrams (Stewart's a wide-eyed, unabashed fan of Star Wars) — and journalists and authors like Fareed Zakaria and Doris Kearns Goodwin. In November 2013, Goodwin was on talking about her book The Bully Pulpit, much to the wonderment of Stewart. "Taft and Roosevelt were thick as thieves and the whole relationship falls apart when they fight each other for the presidency," he marveled. Says fellow late-night host Kimmel: "He built up such trust with his audience, they were willing to tolerate a guest that at face value seemed boring."

He kept Gen Y interested and engaged. Stewart somehow made politics palatable and interesting, with bits like Mess O'Potamia and Indecision 2000. "He changed the way people got their news, that's for sure," Wilmore says. "Before Jon, no one thought of getting their news from a comedy show. He changed the way we view our politicians, that we hold them to a higher standard than we held them before."

He knew when to lay off the humor. In the wake of the horrific shooting at an African-American church in Charleston, S.C., Stewart let the news speak for itself. "I didn't do my job today. I got nothing for you in terms of jokes and sounds because of what happened in South Carolina," he said. For Olivia Munn, who was a correspondent from 2010-11, instances like that stood out because "Jon felt connected to the stories he told. Sometimes there's no jokes."

He gave voice to his own passions. Two of Stewart's pet issues were veterans' rights and animal abuse. he was instrumental in getting compensation for 9/11 first responders who were suffering from health problems, after a bill stalled in the Senate; shortly after Stewart's December 2010 interview with four of the responders, it passed. And in the case of Vick, who was busted for running a pit bull fighting ring, Stewart — himself the owner of a three-legged pit — eviscerated him on air in 2007. "I'd like to cover him in liver and … let the dogs see if he's as fast and elusive as they say he is. My guess is no," said Stewart.

He hastened the end of a series. Stewart went on Crossfire in October 2004, pleaded with hosts Paul Begala and Tucker Carlson to stop being "partisan hacks" and called the show "theater." Crossfire, on CNN, was "hurting America," he told the hosts. "Stop. Stop hurting America." Months later, the show was canceled. On the other hand, he could engage in civil discourse with one of his arch-political opponents, Fox News Channel's "Papa Bear" Bill O'Reilly, who was a guest on the Daily Show. "I asked him if he liked Bill. He said, 'He's a very nice man.' That's because Jon doesn't have hate in him," says Munn.

He spoke out against the Iraq war before it was trendy. In 2002, Stewart winkingly spotlighted "our pending showdown" with Iraq. "It's like they're the Walmart of evil," he called the country after also mocking the elocutionary skills of president George Bush. "Jon questioned the war before a lot of people questioned it. After 9/11 it was very risky," says Wilmore. "He had the courage of his convictions. He frustratingly turns out to be right most of the time. His moral courage made him popular with young people."

He had a friendship of sorts with that dude in the White House. As Politico reported, President Obama realized very early just how influential Stewart could be. So he fostered a close relationship with the comedian, appearing on the show seven times and inviting Stewart to visit him at the White House. Not even Wilmore knew about those sessions. "That came as news (to me). Bob Hope was friends with a lot of different presidents, so it's happened with comedians before. (But) Jon is a (also) critic of them."

This article originally appeared in USA Today. Photo: Dustin Cohen, for USA TODAY