When Johnny Carson announced his retirement, he promised the Tonight Show to David Letterman. However, NBC gave it to Jay Leno instead, resulting in a long time feud between the two. According to the book "The Late Shift", Carson felt betrayed by NBC and Leno. Carson stayed friends with Letterman until his death.
On September 27, 2004, the 50th anniversary of The Tonight Show's debut, NBC announced that Conan O'Brien would take over the show in 2009. Leno was still leading the late-night ratings, but O'Brien was promised the show, so that he would not leave NBC. NBC did not want to lose Leno either, and created The Jay Leno Show (2009), the first nightly network primetime talk show. In 2010, due to poor ratings for both O'Brien and Leno's shows, NBC wanted to move Leno's show into O'Brien timeslot, with O'Brien's "Tonight Show" airing at 12:05 a.m. O'Brien publicly announced that he would rather leave the show than allow that to happen. NBC and O'Brien reached a settlement to allow him to leave the show seven months into his tenure. Leno returned to "The Tonight Show" in March 2010.
The Tonight Show's previous host, Johnny Carson, never once appeared on successor Jay Leno's show. Carson did, however, appear twice on rival late night talk show Late Show with David Letterman (1993) (in a walk-on appearance soon after Letterman's show debuted, and later, in a filmed sketch). In the years following Carson's "Tonight Show" retirement, he reportedly contributed jokes to Letterman's monologues from time to time.
Jimmy Brogan, who co-wrote Jay Leno's opening monologue from 1992-2001, was usually seen sitting off to the side of the audience. Once in a while, Jay would make a bet with Jimmy if a certain joke worked or not, and the loser would pay the winner in front of the camera.
Brandon Tartikoff approached Rosie Odonnell in 1994 about hosting the Tonight Show once a week, on Fridays, as Joan Rivers had done for Johnny Carson. She gleefully accepted; but then got word later that Jay Leno was vetoing the idea because he did not like to take days off. He did not ever let there to be any guest hosts on his program during his reign on the Tonight Show. When an interviewer asked him why he responded "Are you kidding me? That's how I got my job".
For the first three years, when Jay was hosting NBC's "The Tonight Show" at the same time of David Letterman's "The Late Show " on CBS, Letterman regularly beat Jay in the ratings. The turning point came in 1995 when Hugh Grant did an apology tour for his scandal over getting discovered and arrested with call girl Divine Brown. That episode was a hit in the ratings; and Jay maintained a #1 rating from that point on till his cancellation in 2014.