The 2009 TIME 100

When I started as the host of Late Night, someone passed along a great nugget of comedic advice that's been handed down from generations of successful late-night hosts: "You'll use everything you know." Very wise words, as it took me about four shows to do that. Here's one thing I didn't know: this job is hard, man. You have to give it everything you have. You need a work ethic that is second to none. And when I think of work ethic, I think of Jay Leno.

He may not call himself the hardest-working man in show business, but trust me — he is. The job of a late-night host is a grind. To pull it off, you have to give it 120% every night. If you don't, it will show. You can tell that Jay gives it 120% every night because you never notice that he's not. And after his work is done on the Tonight Show, he still does stand-up every weekend.

The thing about Jay — and one of the things I most admire about him — is that it's so obvious that he just loves what he's doing. He loves making people laugh. He loves talking to people. Every night. It's what he is and what he does. And now that he's moving from late night to prime time — 10 p.m. E.T., five nights a week — an even bigger audience will have a chance to enjoy him.

Jay, 59, has been nothing but generous with me regarding his time and advice. But nothing can substitute for the education that comes from just watching him: the way he conducts himself, the way he commands a crowd at a show and the love and effort he puts into it all. That can't be taught — you can only admire it and hope to learn from it. And that's what I aspire to do. Being able to pull off a 100% denim outfit like Jay would be totally awesome too.

Fallon is the host of Late Night with Jimmy Fallon