Late Night is the 12:35am weekday show on NBC. It has had several incarnations with different hosts; all incarnations have had connections to Saturday Night Live.
Late Night with David Letterman (1982-92)[]
Late Night began as a replacement for Tomorrow, a show hosted by Tom Snyder which had followed The Tonight Show since 1973. In the early 80s, instability in the show's format and a contract with Tonight host Johnny Carson that gave him control of the timeslot led to Tomorrow's cancellation.
David Letterman was picked to host the new show, and its first head writer was Jim Downey, then a former SNL writer and featured player who had departed the show after season 5, along with most of the show's cast and writers. Downey is credited with creating Letterman's Top-Ten List, a piece Letterman continued to perform throughout his Late Night run and during his entire tenure on his newer show, CBS' Late Show. Downey departed the show after two years to return to SNL, eventually gaining the position of head writer there.
Late Night with Conan O'Brien (1992-2009)[]
In 1992, a controversy erupted when Letterman was passed over to replace the departing Johnny Carson on Tonight, with the job going to Tonight's resident guest host, Jay Leno. (Leno had hosted SNL in season 11.) An angry Letterman departed for an 11:35pm show at CBS opposite Leno, and the hosting job for Late Night went to Conan O'Brien. O'Brien had been a writer on SNL from seasons 13-16, making occasional onscreen appearances (notably as a deputy restraining Chris Farley in Farley's first appearance); he had left SNL to write for the Fox cartoon series The Simpsons.
A larger SNL connection came with the new show's production. With Late Night's previous producers having left with Letterman to go to CBS, original SNL producer Lorne Michaels was tapped to produce O'Brien's show. He remains the executive producer today.
Late Night with Jimmy Fallon (2009-14)[]
In a situation eerily similar to Tonight's host change a decade and a half earlier, controversy erupted with Tonight again changing hosts. Leno was forced off and O'Brien was named his successor, but the new format lasted only a few months before O'Brien was dropped and Leno reinstated. As a result of the arrangement, O'Brien left Late Night in February, preparing to take over Tonight in June; SNL alum and former Weekend Update anchor Jimmy Fallon was chosen as his replacement. Fallon picked as his announcer Steve Higgins, SNL's current associate producer and writer, who briefly served as head writer during the mid-1990s transition. The Fallon incarnation of Late Night was short-lived, as the still partially-unsettled Tonight hosting conflict ended with Leno being forced off again after five years, with Fallon getting the job.
Late Night with Seth Meyers (2014-present)[]
With Fallon moving to the 11:35pm slot, yet another new host was needed. With Fallon's popularity in the position, Lorne Michaels decided to repeat his earlier move, and tapped then-current Weekend Update anchor Seth Meyers to take the position. The changeover was more sudden than the planned one that marked O'Brien's departure- during the 2014 Winter Olympics, which forced Late Night, Tonight, and SNL off-the-air for most of February, Fallon moved from Late Night to Tonight, and Meyers moved from SNL to Late Night. This required a mid-season SNL and Update cast change, with Colin Jost joining the cast in his place. (With the changeover planned, measures had already been taken to ease the transition, including adding Jost and Rob Klein as co-head writers over the previous two seasons, and adding Cecily Strong to the Update desk at the start of his final half-season.)
Also connecting the current incarnation to SNL is bandleader Fred Armisen, himself an SNL alum who had left the show at the end of the previous season.