Time Warner Inc. is shaking up the leadership at its Turner Broadcasting unit.

Phil Kent, chief executive of Turner Broadcasting since 2003, will give up that title at the beginning of next year to John Martin, Time Warner's chief financial officer. Kent will remain Turner's chairman until his contract expires at the end of next year.

Turner, the parent of cable channels TNT, TBS, CNN, HLN, Cartoon Network and TruTV, is Time Warner's biggest revenue and profit generator.

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Martin's rise positions him as a potential successor to Time Warner Chief Executive Jeff Bewkes, whose contract with the media giant expires in about five years. Martin, in his current post since 2005, has developed a strong financial background, and running Turner should give him operational experience as well.

The shake-up at Turner is the latest executive restructuring within Time Warner and, if recent history is any guide, could lead to more departures.

Earlier this year, sister company Warner Bros. installed a new management team with home entertainment executive Kevin Tsujihara named the successor to longtime Chief Executive Barry Meyer.

The appointment of Tsujihara led to bruised egos and the eventual exits of two other top Warner Bros. executives — television head Bruce Rosenblum and movie chief Jeff Robinov.

In selecting Martin to head Turner, Time Warner passed over several executives, including David Levy, a Turner president who oversees sports, advertising sales and distribution for the cable unit, and Kelly Regal, an executive vice president who worked closely with Kent.

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Other top Turner executives that were potential candidates for Kent's job include Turner Entertainment President Steve Koonin and CNN Worldwide President Jeff Zucker, a former chief executive of NBCUniversal.

Martin, a Time Warner insider, is likely to be viewed as an outsider by Turner, which has its own culture and has not always been cordial to newcomers. That Martin will remain based in New York and not at Turner's Atlanta headquarters may not help matters.

The last time that Time Warner brought in an outsider to run Turner was in 2001, when Hollywood television executive Jamie Kellner was named head of the unit.

Kellner clashed with many Turner executives, and his efforts to get them to work more closely with other parts of Time Warner in the name of corporate synergy backfired. Kellner left in 2003.

Martin is expected to take a more hands-on approach at Turner than did Kent, who was known for giving his team room to roam and for serving as a buffer between Atlanta and Time Warner.

The low-key Kent has spent more than 20 years at Turner and is credited with building TNT, TBS and Cartoon Network into powerful brands.

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Though it has been mostly smooth sailing for him, Kent has hit a few bumps in the road lately, most notably at CNN, which has struggled in the last decade against Fox News and more recently against MSNBC. Kent was seen as resisting a change at the top of CNN to remove its longtime chief, Jim Walton.

As ratings continued to slide last year and pressure for change grew from Bewkes, Walton resigned and Zucker came aboard in January. The hiring of Zucker was seen in media circles as a move advocated by Bewkes.

Although TBS and TNT have big audiences, they also have large programming bills because of the heavy load of expensive sports content on each network. Bewkes has made no secret of his desire to increase the fees that TBS and TNT get from cable and satellite distributors.

But distributors are growing tired of footing the bill for sports programming that a majority of viewers don't watch and are likely to resist increases.

A new Time Warner chief financial officer to replace Martin is expected to be named in the next few weeks.

joe.flint@latimes.com