Larry King's last CNN broadcast tonight

He has interviewed every US president since Richard Nixon, and every celebrity worth the name - plus quite a few who weren't.

But on Thursday night Larry King is hanging up his famous braces, turning off that broad-toothed smile, and shutting down the hour-long interview show that was a feature attraction on cable TV news channel CNN for over 25 years.

There are many reasons for his decision to end one of the longest remaining tenures in major television.

The guy, after all, is 77 years old and underwent a horribly messy divorce scandal recently with his seventh wife, who tried to commit suicide before they resolved their differences and decided to stick together.

But there are also powerful professional reasons to dim the lights on 'Larry King Live', a nightly show that more than any other helped define CNN as the marquee 24-hour international news channel.

Most importantly, the old geezer's laid-back approach to interviewing has been superseded by a tougher more combative and opinionated style personified by the likes of Fox TV's Bill O'Reilly.

After a long career in talk radio, King debuted his show on CNN in 1985.

According to Bob Thompson, a professor of popular culture at Syracuse University, King rarely made history in his interviews, but the sheer mass of over 50,000 interviews will represent a massive trove for future historians studying the period.

"The true legacy of the Larry King Show was the booking department. They had an unmatched ability to get people who were at the centre of the zeitgeist," said Thompson.

Indeed, his most memorable shows blurred the line between human interest and politics. On his show even Margaret Thatcher sounded normal, Marlon Brando seemed relaxed and Monica Lewinsky gave her first interview about her relationship with former president Bill Clinton.

King often boasted of his lack of preparation for interviews as a way of ensuring he would ask the simple questions the public was interested in. But critics claimed that the lazy technique prevented him from getting to the heart of many issues, and left King open to charges of ignorance.

But as they say, all things must to an end. So has this..