NEW YORK - Outside Studio 6B at 30 Rockefeller Plaza, the once and future home of "The Tonight Show," the smell of fresh paint and sawdust fills the air. Visitors to one of the last tapings of "Late Night With Jimmy Fallon" are led up a back staircase by an NBC page, winding carefully past dusty drop cloths and dumpsters piled with construction waste.

It's just a matter of days until the launch of "The Tonight Show Starring Jimmy Fallon," and if NBC's hive-like headquarters aren't quite ready, Fallon most definitely is.

"Let's do it! We're all just ready to unleash," he says. After nearly a year of anticipation and a months-long publicity blitz, the comedian is eager to get started on his new gig Monday night. "Everyone here's so pumped and excited."

"Excited" is a word that comes up frequently in conversation with Fallon. At 39, Fallon is enthusiastic bordering on hyperactive, bouncing from topic to topic and speaking in near-constant hyperbole.

This optimistic energy is sure to come in handy at "Tonight," where he will become just the sixth host in the 60-year history of the venerable franchise. Particularly after the acrimonious Late Night War of 2010, all eyes will be on Fallon to see if his tenure is more successful. He remained studiously neutral throughout the debacle that ended with Conan O'Brien's departure from "Tonight" after just seven months, and despite what some have seen as passive-aggressive griping by Leno, the handover this time around has been handled gracefully.

"Jay's been totally supportive," says Fallon. "We're friends, as much as we can be living on different coasts. He calls me every couple weeks, just to check in, like, 'Hey, hanging in there, buddy?'"

When Leno signed off on Feb. 6, he was still the top-rated host in late-night television. And while "Tonight" remains the marquee brand, the competition for eyeballs is fiercer than ever. At last count there are at least 13 other cable, network and syndicated late-night talk shows on the air, including "Jimmy Kimmel Live," "The Colbert Report" and "Conan."

Fallon at least left "Late Night" with a bang: His Feb. 7 swan song drew the highest ratings the show has seen since David Letterman signed off in 1993.

And the comedian is determined to maintain a healthy attitude in the face of inevitable scrutiny. "I'm sure the ratings will be big for the first week after the Olympics," he says, "and then they'll go down and people will say, 'Fallon lost 40 percent of this viewers, this is terrible.' I'm preparing myself for that roller coaster. Don't believe the good stuff, and don't believe the bad stuff."

When Fallon made his "Late Night" debut, few if any could have predicted he'd ascend to the "Tonight" throne in just less than five years. O'Brien, his predecessor, had just been promoted to 11:35 after 16 years and a protracted, five-year transition of power from Leno.

At the time, Fallon, a former breakout star on "Saturday Night Live," where he co-anchored "Weekend Update" with Tina Fey and played memorable characters such as obnoxious IT guy Nick Burns, was rebounding from a lackluster attempt at a film career, starring in the flops "Taxi" and "Fever Pitch."

At first, it was far from obvious that Fallon was cut out for late-night TV, either. His premiere garnered mixed reviews, with his nervous monologue and uncertain interviewing skills drawing nearly unanimous criticism.

But over its freshman year, the show quietly blossomed, drawing on Fallon's arsenal of impressions and musical abilities and capitalizing on its house band, the Roots.

A turning point came when Fallon hosted the Emmys in 2010. His energetic turn - he opened the show with a rousing performance of "Born to Run" featuring Fey, Jon Hamm and the cast of "Glee" - is the moment when viewers and critics alike realized he might be pretty good at this hosting thing.

Since then, even for viewers who don't stay up until 12:37 a.m., it's been difficult for anyone with an Internet connection to ignore that Fallon is up to something different. He's "slow-jammed the news" with President Barack Obama. He's presented the "Evolution of Mom Dancing" with Michelle Obama and "The History of Rap" in four parts with frequent collaborator Justin Timberlake.

"I love the fact that here you have a guy who's going to be hosting 'The Tonight Show' who can almost claim Justin Timberlake and Bruce Springsteen as members of his rep company," says David Bianculli, founder of the website and a professor of TV and film at Rowan University in Glassboro, Gloucester County. "That's a whole different sort of animal."

Predicts Bianculli, "I think Fallon will compare very favorably with Jay because his stuff is so much more clever and so much more vibrant. It's 'The History of Rap' versus 'Headlines.' That's a generational difference."

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