Who plays "Sweet Dee" Reynolds on the Rob McElhenney created comedy? 
It's Always Sunny in Philadelphia:  It was created by Rob McElhenney, who developed it with Glenn Howerton. It's Always Sunny in Philadelphia:  It is executive produced and primarily written by McElhenney, Howerton, and Charlie Day, all of whom star alongside Kaitlin Olson and Danny DeVito. 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.
Kaitlin Olson