Jay Leno spent 17 years as ` ` Tonight Show '' host Friday . Leno has been criticized for letting down the audience , but he 's been No . 1 for years . He will be succeeded by Conan O'Brien ; in fall , he 'll leave prime - time altogether .
Jay Leno concludes 17 years as `` Tonight Show '' host Friday . Leno has been criticized for dumbing down the show , but he 's been No . 1 for years . He 'll be succeeded by Conan O'Brien ; in fall , he 'll launch prime-time show .