Kaitlin Olson began her career in a theater troupe.
Kaitlin Olson . She began her career in the Groundlings , an improvisational group in Los Angeles , California , and had minor roles in several television series before being cast as Deandra `` Sweet Dee '' Reynolds on the FX black comedy series It 's Always Sunny in Philadelphia in 2005 . The Groundlings are an improvisational and sketch comedy troupe and school based in Los Angeles , California . The troupe was formed by Gary Austin in 1974 and uses an improv format influenced by Viola Spolin , learning her improvisational theater techniques from the Second City 's Del Close , to produce sketches and improvised scenes .