. >>> when stephen kobe take colb to the "late show with letterman" he'll leave that thinking behind.t's not all laughter from critics. here's cnn alexandra field. >> i've got to tell you, i do not envy whoever they try to put in that chair. >> reporter: stephen colbert is he ready to take the microphone from david letterman jb the 2015 transition marking the end of a late show era. >> paul and i will be wrapping things up and taking a hike. >> reporter: but colbert's new beginning will also mark another kind of ending. he plans to retire stephen colbert the character. the conservative pundit he place on comedy central the "the coal bae report." >> there is no bigger fan of bill o'reilly than bill himself. but -- i am a close second. ♪ >> reporter: the routine has won him plenty of fans and, yes, critics, including real-life conservative rush limbaugh. >> cbs is just declared war on the heartland of america. they've hired a partisan so-called comedian. to run a comedy show. >> colbert has been mocking conservatives a decade. i'm not surprised rush limbaugh isn't happy with the choice