Brian Stack (born August 18, 1967) is an American actor, comedian, and writer best known for his sketch comedy work on all three Conan O'Brien late-night talk shows, previously working on Late Night with Conan O'Brien and The Tonight Show with Conan O'Brien, and on O'Brien's current talk show, Conan on TBS. Stack left Conan in April 2015 to join the writing staff of the CBS series The Late Show with Stephen Colbert.