David Letterman's plans to retire next year have already touched off a guessing game about his successor.

David Letterman’s plans to retire next year have already touched off a guessing game about his successor.

David Letterman’s plans to retire next year as host of his long-running show “Late Night with David Letterman,” has begun to fuel speculation on a successor to go head-to-head against Jimmy Fallon on “The Tonight Show.”

Dave’s departure in 2015 has already boosted Fallon. He’ll be the undisputed king of late night talk until Dave’s successor is crowned.

Then the race will be on in earnest to battle for younger audiences the networks crave.

A number of obvious names have already surfaced, along with some not-so-obvious ones. Topping the list, of course, is Conan O’Brien, whose late-night cred is firmly establish.

He had a six-year run (2003-2009) as Jay Leno’s backup on “Late Night with Conan O’Brien.” In fact, Fallon replaced him when he moved up to the “Tonight Show.”

For a brief shining moment O’Brien commanded the flagship of late night television talk as Leno’s successor–until NBC started toying with the line-up and pushed O’Brien back a half hour to give Leno a seat back at the table.

O’Brien left in a huff for the hinterlands of cable television in 2010. He’s had his own show on TBS since then. At 50, he’s still young enough to attract younger viewers.

During his stint on TBS Conan has matured as a talk-show host. He’s more laid back and less frenetic than he was during his early days behind a desk. And he’s genuinely funny and creative.

Craig Ferguson, 51, who’s been Dave’s understudy since 2005 on “The Late, Late Show With Craig Ferguson,” is also a logical successor. The Scottish-born comedian has developed his own brand of off-beat humor. And, he could argue that CBS owes it to him. He replaced Craig Kilborn.

Jimmy Kimmel, who has a late, late show is also a logical choice. But whether he’d want to leave his comfortable roost at ABC remains to be seen.

With Dave leaving, however, CBS may come under pressure to break the hold white men have had on late night talk going back to the 1950s.

The may create an opening for someone like Chelsea Handler, who just left her show “Chelsea Lately,” on the E! network. Her potty-mouth brand of humor, however, may not go over well with the suits on commercial television.

Ellen DeGeneres is also a possibility but it’s hard to see her leaving her daytime show, now that Oprah is gone.

Arsenio Hall, Jon Stewart and Stephen Colbert have also been dropped as possible replacements, although it’s hard to see how Stewart’s and Colbert’s humor would work.

Other less obvious choices include Carson Daly and Ryan Seacrest. Both are younger than Ferguson and O’Brien and might relate better to younger audiences.

Drew Carey, who has established himself on CBS daytime as host of “The Price is Right” is also being mentioned as a contender.

That just about rounds out the list of early candidates, except for one… Jay Leno.

Leno didn’t act like he was ready to leave when NBC announced Fallon as his replacement, and he was still No. 1 in the ratings. He could really upset the applecart if the once (and future?) king of late night decides to reclaim his throne.