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(CNN) - Host Jay Leno leaves "The Tonight Show" this evening, occupying an odd perch in entertainment.
"We've all fought and kicked to make this network fifth place, we're counting on you Jimmy! Don't let it slip to 6th!" Leno joked.
The late night comedian has often been critically assailed, but the show is an undisputed number one as he hands it off to Jimmy Fallon, who was just 17 when the now 63-year-old Leno got the full time job as "Tonight Show" host.
So why has Leno's reign as king of late night often seemed stormy? He is after all an up-from-his-bootstraps, American success story. Leno evolved from hard-working stand-up comedian, to a guest on "Late Night with David Letterman," to the host of NBC's most bankable late night franchise.
"The Tonight Show" draws nearly 4 million viewers a night, the highest ratings in its time slot. But Jimmy Kimmel, one of his competitors, told CNN that Leno sold out.
"I do think (Leno) is capable. I've seen him. I mean, listen, you know, the guy is one of the great comedians," Jimmy Kimmel told CNN's "The Lead with Jake Tapper" last year.
But asked if Leno dumbed down his material, Kimmel said: "Yes, I think so. Yes, I mean, I think that's fair to say."
But Leno's controversies go far beyond his jokes. Some of the more infamous stories about him began when both he and critics' darling Letterman competed to replace the legendary Johnny Carson.
The jockeying and in-fighting became legendary, as captured in Bill Carter's best selling book "The Late Shift." The book was made into a 1996 HBO movie, which featured a portrayal of a true story: Leno hiding in a closet, eavesdropping on a meeting of executives discussing who would replace Carson, showing Leno's tenacity or ruthlessness, depending on your point of view.
Leno, of course, got the gig.
The real maelstrom began in 2009, when NBC moved Jay Leno to the prime time slot. Conan O'Brien then slid into "The Tonight Show" spot, a deal that had been announced five years before.
Letterman and his counterparts joked endlessly about the not-so-nice hand off to Conan.
Leno went to 10 p.m., which didn't work. Conan complained that the show hurt his ratings. Ultimately it became a confusing mess. Leno went back to his previous job, and a very angry Conan left NBC with a $45 million buyout before landing at CNN’s sister network, TBS.
Both Letterman and Kimmel had field days mocking Leno for duplicity. Trying to be a good sport Leno invited Kimmel on his show.
"What's the worst trick you ever played on someone?" Leno asked Kimmel.
"I told a guy that 'Five years from now, I'm going to give you my show.' And then when the five years came, I gave it to him. And then I took it back almost instantly," Kimmel said.
And yet, Leno returned, as did his ratings at 11:30 p.m. Punch after punch, Leno stayed standing, and winning.