When Conan O'Brien was hired to replace David Letterman on NBC in 1993, nobody thought the gangly unknown could hack the same talk show tumult that sank Chevy Chase. The former writer for "Saturday Night Live" and "The Simpsons" had virtually no history of performing and his comedy bordered on the surreal and nonsequitur. But 20 years later (as of October this year), Brookline's native son is still going strong -- despite that brief and tumultuous stint as host of "The Tonight Show." Along with talented staff writers like Robert Smigel and Louis C.K., Conan has given us some of our best sketch comedy. With several notable guests coming up this month and in honor of Conan's 20 years, here are 12 of his most memorable recurring bits from late night.