Jay Leno has hosted Tonight since 1992

Offbeat comic Conan O'Brien will become the fifth host of the television institution in 2009.

Leno, 54, broke the news to viewers during a special programme on Monday to mark the 50th anniversary of The Tonight Show.

Leno took over the show in 1992 from legendary host Johnny Carson, who fronted the show for 30 years.

Contract

Bosses at the NBC network were anxious to hold on to 41-year-old O'Brien, whose late-night chat show is aired directly after The Tonight Show.

O'Brien's contract with NBC was due to expire this year.

The last time the a former Saturday Night Live comedy writer was up for a renewal, Fox tried to lure him with an earlier show, but O'Brien turned it down at the last minute.

Shortly after he signed his latest contract extension, Leno said NBC executives approached him, saying they did not want to lose O'Brien.

Carson tribute

He endorsed the move and set his own 2009 exit date, when he will be 59.

Leno also offered a warm tribute during his show on Monday to Carson by showing a lengthy clip package of his funniest moments.

"Johnny set the standard for how this job should be done," he said.

"He was such a gentleman. He always had impeccable timing. He was the comedian's comedian.

"Those of us who do this for a living, we all owe him a tremendous debt."