Jon Stewart said Tuesday that he would step down from Comedy Central’s “The Daily Show” after 17 years, leaving a new hole in the ranks of latenight television and setting up another challenge for the Viacom-owned cable network, which recently bid farewell to popular timeslot host Stephen Colbert.

Stewart’s current contract is believed to end around the fall of 2015, but the time of his departure is uncertain. He told viewers on Tuesday night’s broadcast the he might leave as early as July or perhaps stay until sometime in December. “Daily Show” has run on Comedy Central longer than any other program except for the animated “South Park.”

The news is not entirely surprising. Stewart, 52, had discussed the possibility of leaving “The Daily Show” while promoting “Rosewater,” a film that marked his directorial debut. And yet, his departure means that the backbone of Comedy Central’s lineup is looser than it has been in some time. The network in January launched “The Nightly Show,” starring producer and writer Larry Wilmore, as a successor to Colbert’s “Colbert Report,” which ended in December.  Colbert will succeed David Letterman on CBS’ “Late Show” later this year.

Comedy Central executives have quietly been planning for his exit. “I don’t like to think about the day that Jon leaves, but there will be a day. The show will live on. It is a franchise, like the ‘Tonight Show,'” Michele Ganeless, Comedy Central’s president, told Variety in December. “We’ll figure it out when we get there. He has set the standard. We will identify talent, and hopefully, we will find the next Jon Stewart.”

Stewart’s departure represents another kind of loss for Comedy Central. He played a key role in discovering and promoting new talent. Indeed, Colbert and Wilmore were contributors to the program before network executives saw them as talent that could anchor their own programs. Stewart’s Busboy Productions is a producer of “Nightly,” and is expected to remain affiliated with that program. Stewart also gets some credit for the rise of John Oliver, the British comedian who recently moved to HBO after a successful stint filling in for Stewart while he worked on his movie.

Under his aegis, “Daily Show” has become a go-to destination for young viewers between 18 and 34, and is considered by many in that crowd to function as a different kind of news broadcast. Stewart, who riffs on the day’s events before showcasing pieces from contributors, interviewing authors and celebrities and winding up with a video snippet called “Your Moment of Zen,” has never been shy about using his desk to deliver scorching indictments of “real” newsgathering operations like CNN and CNBC.

When Stewart joined “The Daily Show,” he faced questions similar to the ones that will challenge his successor. The half-hour program began in July 1996, and it was originally hosted by Craig Kilborn and was created by Lizz Winstead and Madeleine Smithberg.  The program was originally conceived as a way to fill the hole left by the departure of “Politically Incorrect,” a gimlet-eyed take on current events hosted by Bill Maher.

That show was moving to ABC  and, as Doug Herzog, president of Viacom Entertainment Group, recalled in  a December interview with Variety, “It was crushing news, but we had a year” to come up with something different. The operating idea in executives’ heads was “we’ve got to be funny every day, because otherwise we’re just ‘Benny Hill’ reruns. What can we do?” recalled Herzog, who led Comedy Central at the time.

Stewart would join the show in 1999, and make it more politically focused. Under Kilborn, the program held more true to a “fake newscast” format. Stewart, who had a talk show at MTV as well as a short-run Comedy Central series, would use the 2000 election to tilt the program more toward issues.