The widely acclaimed US show has been credited with taking the genre of satirical journalism to new heights, becoming an important element in US political discourse since Stewart took over from original host Craig Kilborn in 1999.

Stewart's shock announcement made news waves around the globe, showing the comic relief and analysis in which he frames world events has proved a draw beyond US shores.

The French newspaper carried a story on Stewart's plans, as did , Britain's Sky News, papers in Israel and the .

Self-styled fake news anchor Stewart has not said when he will leave the show this year, or what he plans to do next.

"This show doesn't deserve an even slightly restless host and neither do you," he told his gob-smacked audience last week. The father of two added he had "a lot of ideas, a lot of things in my head. I'm gonna have dinner. On a school night. With my family. Who I have heard, from multiple sources, are lovely people."

Stewart and have won 20 Primetime Emmys over the years, as well as numerous other awards for his ability to dig with delight into global events large and small, finding humour through four US presidential election cycles and administrations Republican and Democrat.

The show has become a key stopping point for American political leaders, including President Barack Obama, Hillary Rodham Clinton and Senator John McCain, and more international guests like Malala Yousafzai, the Pakistani teenage Nobel Peace winner waging a battle against terrorists, and off-beat London Mayor Boris Johnson.

Stewart offers an unabashedly liberal political slant, but is non-partisan in his satire, and has poked fun at Obamacare as well as right-wing commentator Bill O'Reilly.

His departure comes with the US news media in a state of re- examination after the announcement that National Broadcasting Co television anchor Brian Williams had been suspended for six months for apparently fudging an account of his experience a decade ago covering the war in Iraq. Williams seemed to have misremembered that he wasn't, as he had declared repeatedly, shot out of the sky in a military helicopter.

Wearing a woeful expression last week, Stewart summed up everyone's befuddlement with crystalline efficiency on the topic. "Bri! Why? Why, Bri? Why lie? Sigh," he said, following his silly rhyme with a shrewd diagnosis for what might have led Williams to muddle his Serious News cred with habitual visits to any talk show (including ) that would have him.

Stewart called it Infotainment Confusion Syndrome, a brain misfire that occurs, he said, "when the 'celebrity cortex' gets its wires crossed with the 'medulla anchor-gata'".

He mocked the mediaverse for obsessing over Williams' alleged misdeeds: "Finally is being held to account for misleading America about the Iraq war."

"Never again," Stewart added dramatically, "will Brian Williams mislead this great nation about being shot at in a war we probably wouldn't have ended up in, if the media had applied this level of scrutiny to the actual [bleep] war."

New Jersey-raised Stewart, 52, was born Jonathan Stuart Leibowitz but later changed his name to Stewart. His roots are in stand-up comedy, not the news industry. Over the years he has dabbled with other endeavours in film and acting and has also written several books.

In 2013 he made a deep-dive into foreign turf to direct , a film about an Iranian-born journalist imprisoned for 118 days in Tehran and accused of being a spy.

Also in 2013, Jewish Stewart travelled to Cairo for a guest appearance - posing as a scruffy, captured foreign spy - on the TV show of Egypt's answer to Stewart, Bassem Youssef, who appeared on the New York-based programme.

Youssef's show (Arabic for "The Programme") was cancelled last June with the comedian saying ominously that Egypt's climate was not "suitable" to satirising the powerful.

The political climate was never Jon Stewart's problem. He has fed on it, big-footing his way through the most delicate diplomatic territories.

Stewart's routines have frequently played on news and entertainment shows in Israel.

In a well-known skit, Stewart is accused by Palestinians of being pro-Israel and by Israelis of being pro-Palestinian.

But is not just fun and games. Media researchers have discovered that satirical programmes like Stewart's often informed viewers better about important topics than traditional newscasts.

According to figures released by the Pew Research Centre, the median age of Stewart watchers was 36 - or about 15 years younger than most cable news shows in the United States.

Stewart and the show "made the news more relevant for a lot of young people", said Ken Paulson, president of the Newseum's First Amendment Centre and former editor-in-chief at .

"It created an incentive for people to learn more about the world around them."

He said Stewart's appeal was based on his ability to show that the news matters to people.

"He conveyed every night that this was not a civics lesson, that the news had something to do with the way we live and what we value," Paulson said.

"That's the challenge for traditional news media. They need to convey why news matters."

While the genre of satirical news is not new, "Stewart did it better than anyone else," said Dan Kennedy, a journalism professor at Northeastern University in Boston. "He just seemed to have a smarter and more analytical take on the news than any of the predecessors, and as a result, I think Stewart emerged as our most perceptive media critic."

Bruce Hardy, a researcher in political communication at the University of Pennsylvania's Annenberg Public Policy Centre, said Stewart's show and its spin-offs in essence created a new kind of news programme.

"We used to have a few minutes of satire on the late-night talk shows, but to have an entire half-hour programme of satire on the news, that's a new genre which has emerged in the past 15 years," Hardy said.

Kennedy said: "He came along at time when the media were fracturing into many different audiences. He was able to take advantage of that and he developed his own audience."