Gary Levin

USA TODAY

NEW YORK — "I'm Jimmy Fallon, and I'll be your host ... for now."

That's how the sixth Tonight Show star in 60 years cheekily welcomed viewers Monday as NBC's storied — and at times turbulent — late-night franchise ushered in a generational shift. He's remade the top-rated show, which (apart from Conan O'Brien's brief 2009 run) has been unchanged since Johnny Carson made it essential.

Fallon, 39, presided over Tonight's return to 30 Rock for the first time since 1972, replacing Jay Leno, 63, who exited Feb. 6 (for the second time) after a 22-year run. "I really don't know how I got here," said Fallon, who appeared on Saturday Night Live and hosted Late Night for the past five years. With his parents in the audience and infant daughter backstage, he reintroduced himself, his band, The Roots, and announcer Steve Higgins to viewers, proudly displaying a four-leaf clover etched into the floor of Studio 6B, where he delivered an opening monologue chock-full of Olympics jokes.

Will Smith and Fallon did some hip-hop dance moves, and Smith called the night "really huge." U2 performed Invisible on the rooftop, with the city's skyline as a backdrop at sunset, and later sang an acoustic version of Oscar nominee Ordinary Love.

And after vowing to collect on a $100 bet from "my buddy ... who said I'd never be the host of The Tonight Show," Robert De Niro walked onstage, thrusting a Benjamin at Fallon, followed by a parade of bill-toting celebrities including Tina Fey, Joe Namath, Mariah Carey, Tracy Morgan, Joan Rivers, Kim Kardashian, Lindsay Lohan, Mike Tyson, Lady Gaga and — finally — Stephen Colbert, who dumped a metal bucket full of pennies on Fallon before taking a selfie with him and bellowing, "Welcome to 11:30, bitch!"