Kaitlin Willow Olson, an American actress and comedian, played Deandra "Sweet Dee" Reynolds on a popular black comedy series on what network?
It's Always Sunny in Philadelphia: It's Always Sunny in Philadelphia is an American television black comedy sitcom that premiered on FX on August 4, 2005. Kaitlin Olson: Kaitlin Willow Olson (born August 18, 1975) is an American actress and comedian. 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.
FX