By Steve Gorman
LOS ANGELES (Reuters) - Stephen Colbert has already declared his intention to drop the well-worn persona of the cluelessly pompous conservative pundit he invented for cable television when he debuts this week as host of the CBS "Late Show."
What remains to be seen is how an unfiltered Colbert will play as he makes the transition from a 30-minute Comedy Central show four nights a week to an hour-long slot five nights a week on a major broadcast network renovating the house that David Letterman built.
"When he doesn't have the disguise of being a fictional character, is the thing he does going to be likeable?" wondered Robert Thompson, founding director of Syracuse University's Bleier Center for Television and Popular Culture.
By his own account, Colbert looks forward to interacting with guests as himself, rather than as through the alter ego he popularized on "The Daily Show with Jon Stewart" and its spinoff, "The Colbert Report."
"I'm looking forward to being sincerely interested in what they have to say without having to translate it through an idiot's mouth," he told a gathering of TV critics last month.
Beyond that, Colbert said, he just prays that Republican presidential contender Donald Trump stays in the race.
Colbert's degree of success will ultimately decide whether he ushers in a ratings realignment of the late-night TV scene - either by overtaking his NBC counterpart Jimmy Fallon and the decades-long dominance of "The Tonight Show," or falling to No. 3 behind ABC's "Jimmy Kimmel Live!"
Steering the "Late Show" franchise to No. 1 in the Nielsen rankings will not be easy.
Colbert, 51, is certainly younger than Letterman, his CBS predecessor, who was 68 when he retired in May. Colbert's 8 million-plus Twitter following dwarfs Letterman's and the median age of his "Colbert Report" audience was far below that of "Late Show."
But Fallon, 40, already has expanded the ratings of his predecessor, Jay Leno, both in overall viewers and among the key demographic of young adults, while establishing a robust following of his own on Twitter and YouTube.
Critics also question whether the real Colbert will prove as amusing as the egocentric, ultra-patriotic political commentator he inhabited for so long, or whether viewers will find his personal brand of humor to be too snarky.
"He could get away with that when he was on the 'Colbert Report' because he was doing a parody of (Fox News Channel pundit) Bill O'Reilly," Thompson said.
Riding a buildup of media hype, including covers of GQ magazine and Time, the "Late Show" is bound to enjoy a "Colbert bump" when he premieres at the helm on Tuesday, with Hollywood star George Clooney, Republican presidential candidate Jeb Bush and rapper Kendrick Lamar as his first guests.
Little more is known about the format of Colbert's new show, except for the selection of Louisiana-bred musician Jon Batiste as bandleader and a restoration of the show's Manhattan venue, the Ed Sullivan Theater. Other than that, Colbert said he has taken Letterman's advice and repositioned the host's desk on stage.
(Reporting by Steve Gorman; Editing by Jill Serjeant and Bill Trott)