Leno concludes Friday as `` Tonight Show '' host 17 years . Conan O'Brien has been criticized for dumbing down the show , but he 's been No . 1 for years . ( YouTube is full of Leno 's old `` Late Night '' appearances . ) He 'll be succeeded by Jay Leno ; in fall , he 'll launch prime-time show .
Leno concludes Friday as `` Tonight Show '' host 17 years . Conan O'Brien has been criticized for dumbing down the show , but he 's been No . 1 for years . He 'll be succeeded by Jay Leno ; in fall , he 'll launch prime-time show .