A handful of potential successors have already emerged to take over for Larry King when he leaves his prime-time CNN interview show sometime this fall.

All have their strengths and weaknesses — if they can even be convinced that the job is right for them.

But what CNN U.S. President Jon Klein could use is someone to shake up the mix, a candidate no one has anticipated that will make people sit up and take notice. The choice will likely define Klein’s legacy at CNN, one that is troubled now because of the continued ratings dominance of Fox News Channel and the emergence of MSNBC as a colorful competitor.

He has indicated that he wants a new show that doesn’t stray far afield from King’s mission.

“We will continue to do a provocative, topical, intelligent newsmaker interview show every night,” he said, “but the format and the style is going to depend a lot on the host — their interests, their style, their approach. Step one is get a host and build the show around them.”

None of CNN’s competitors have a similar show, he said. “It’s an important tool in the arsenal and we want to keep it going,” he said.

That would seem to eliminate the idea of moving Anderson Cooper’s 10 p.m. ET program up an hour. Cooper has carved out an aggressive news persona, quick to travel to the scene of news and, in the oil spill story, aggressively go after BP. He also has ratings problems, and may not wish to change direction to appeal to King’s audience.

King’s anniversary week lineup of guests — President Barack Obama, LeBron James, Bill Gates and Lady Gaga — illustrated a versatility that’s not easy to come by. His simple interview style often has been derided, but not everyone can be equally comfortable with presidents and pop stars.

CBS News anchor Katie Couric has been the most frequently mentioned potential successor, in part because of the skill she displayed as an interviewer on the “Today” show, which is underused in her CBS job.

“There are a lot of potential hosts of this sort of show,” Klein said. “There aren’t a ton of them; there are a finite number of them. Katie is certainly one of them.”

Couric would have a huge challenge, though. It could not have been easy moving to CBS and being perceived as a savior for a third-place news show — one that’s still in third place. Moving to CNN and facing the same pressure at a much smaller network would be a tough sell.

Several published reports say CNN has expressed interest in Britain’s Piers Morgan. He’s supposedly shown skill as an interviewer overseas; most Americans know him only as someone who judges amateur singers and dancers on “America’s Got Talent.”

King’s favored successor is Ryan Seacrest.

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