Stephen Colbert is CBS' top choice to replace the retiring David Letterman, and has indicated that he's willing to take over the Late Show when the time comes, people familiar with both sides of the discussions tell Mashable.

Colbert has not had any formal contract discussions with CBS, and no agreement is in place, but sources tell Mashable that he first engaged with network executives while Letterman was still mulling the timing of his retirement. Though CBS has had conversations with other candidates, including Colbert's Comedy Central counterpart Jon Stewart, individuals with knowledge of the situation say Colbert is currently the front-and-center candidate.

A CBS spokesman told Mashable: “We’re not commenting on any rumors or speculation about succession.” Comedy Central had no comment.

Colbert's contract to host The Colbert Report on Comedy Central runs through the end of 2014, which would free him up in time to move over to CBS when Letterman ends his 33-year run in late-night TV. Letterman left the exact date of his departure vague while announcing his retirement plans on Thursday.

“We don’t have the timing of this precisely down; it will be at least a year or so," Letterman said on Thursday's episode of the Late Show. "But at some time in the not-too-distant future — 2015, for the love of God."

Colbert would leave behind the pseudo-conservative persona he's cultivated at The Colbert Report and just be himself at his CBS home, one of the individuals told Mashable. He has stepped out of character on rare occasion, though not on his show, and possesses the same wry, incisive interview skills that Letterman has showcased for decades.

A few questions remain for CBS in its pursuit of Colbert; money is a big one. The gap between a potential network payday and a Comedy Central salary has significantly narrowed in recent years. Plus, Colbert is meticulously topical in his selection of guests, many of whom aren't stars, but the Late Show gig would force him to shoot the breeze with all manner of celebrities peddling movies and TV shows. That isn't to say he wouldn't do it well — but would he want to?

There's also more of a workload: five nights a week to cover an hour, versus four nights doing 30 minutes. But in the end, the draw of being Letterman's replacement could be too strong for Colbert, who is a friend and admirer of Letterman's.

These conversations represent the state of play at this time, but anything can happen in Letterman's remaining year. Twitter and Facebook were filled with calls to diversify the mostly white male late-night lineup, and Colbert still has more than eight months left on his Comedy Central contract.

Other names that have come up in discussions for Letterman's replacement have included Neil Patrick Harris, who just finished up How I Met Your Mother on CBS, and Craig Ferguson, who comes on after The Late Show With David Letterman. Harris could remain a wild card, but Ferguson, though well-liked by the network in his later slot on The Late Late Show With Craig Ferguson, has never been seen as the heir apparent.

At one point, Stewart was seriously considered for the Late Show post, but his prospects have steadily faded over time as sentiment coalesced around Colbert. The Daily Show host has finished shooting his feature film directorial debut Rosewater, and is said to be passionate about continuing that and other off-air pursuits, which a major late-night hosting job would not easily permit.

CBS is a cousin of Comedy Central via Viacom, from which the broadcast network was spun off in 2006. Stewart and Colbert enjoy similar ratings, but The Daily Show is still considered Comedy Central's flagship program, which would make a Stewart poach potentially more fraught. Colbert, who will celebrate his 50th birthday next month, made his bones as a correspondent on Stewart's show, leaving in 2005 to start his spinoff series that immediately follows it; the shows have essentially gone hand-in-hand ever since, with the two hosts joining forces for special election coverage and other events.

The Colbert Report has won Emmys for writing for a variety, music or comedy program in 2008, 2010 and 2013; it won its first outstanding variety series Emmy last year, snapping a 10-year run for Stewart's show.

Though CBS has been quietly lining up his replacement for months, by all accounts, Letterman's decision to leave was entirely his own, and was largely telegraphed when he signed a one-year contract extension to remain through 2015. Since then, the 66-year-old Letterman had been having ongoing conversations with CBS CEO Leslie Moonves, who released the following statement after Letterman's announcement Thursday:

When Dave decided on a one-year extension for his most recent contract, we knew this day was getting closer, but that doesn’t make the moment any less poignant for us. For 21 years, David Letterman has graced our Network’s air in late night with wit, gravitas and brilliance unique in the history of our medium. During that time, Dave has given television audiences thousands of hours of comedic entertainment, the sharpest interviews in late night, and brilliant moments of candor and perspective around national events. He’s also managed to keep many celebrities, politicians and executives on their toes – including me. There is only one David Letterman. His greatness will always be remembered here, and he will certainly sit among the pantheon of this business. On a personal note, it’s been a privilege to get to know Dave and to enjoy a terrific relationship. It’s going to be tough to say goodbye. Fortunately, we won’t have to do that for another year or so. Until then, we look forward to celebrating Dave’s remarkable show and incredible talents.

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