It's Always Sunny in Philadelphia is an American independent sitcom that premiered on FX on August 4, 2005. New episodes continue to air on FX, with reruns playing on Comedy Central, general broadcast syndication, and WGN America—the first cable-to-cable syndication deal for a sitcom. The show was created, developed, and produced by Rob McElhenney, Glenn Howerton and Charlie Day, all of whom star in the show. The series follows the exploits of "The Gang," a group of self-centered friends who run Paddy's Pub, a relatively unsuccessful Irish bar in South Philadelphia, Pennsylvania.

The series follows "The Gang", a group of five depraved underachievers: twins Dennis Reynolds and Deandra "Sweet Dee" Reynolds; their friends Charlie Kelly and Ronald "Mac" McDonald; and Frank Reynolds, Dennis and Sweet Dee's father (although not biologically, it is revealed). They run the dilapidated Paddy's Pub, a bar in South Philadelphia. They are often dishonest, petty, egotistical, selfish, greedy, unethical, lazy, manipulative, deceitful, hypocritical, self-centered, vain, disloyal, unremorseful, hasty, overly competitive, immature, vengeful, and arrogant. Episodes usually find them hatching elaborate schemes, conspiring against one another and others for personal gain, vengeance, or simply for the entertainment of watching one another's downfall. They inflict physical and psychological pain. They regularly use blackmail to manipulate one another and others outside of the group.

Philadelphia ( /ˌfɪləˈdɛlfiə/) is the largest city in the Commonwealth of Pennsylvania and the county seat of Philadelphia County, with which it is coterminous. The city is located in the Northeastern United States along the Delaware and Schuylkill rivers. It is the fifth-most-populous city in the United States, with a population of 1,526,006 as of the 2010 U.S. Census. Philadelphia is also the commercial, cultural, and educational center of the Delaware Valley, home to 6 million people and the country's fifth-largest metropolitan area. The Philadelphia metropolitan division consists of five counties in Pennsylvania and has a population of 4,008,994. Popular nicknames for Philadelphia are Philly and The City of Brotherly Love, the latter of which comes from the literal meaning of the city's name in Greek (Greek: Φιλαδέλφεια ([pʰilaˈdelpʰeːa], Modern Greek: [filaˈðelfia]) "brotherly love", compounded from philos (φίλος) "loving", and adelphos (ἀδελφός) "brother").

Charles Peckham "Charlie" Day (born February 9, 1976) is an American television and film actor and writer best known for playing Charlie Kelly on It's Always Sunny in Philadelphia.

Day was born in New York City. His mother, Mary (née Peckham), is a piano teacher at The Pennfield School in Portsmouth, Rhode Island. His father, Dr. Thomas Charles Day, is a professor of Music History and Music Theory at Salve Regina University in Newport, Rhode Island.

Charlie Day spent most of his childhood in Middletown, Rhode Island. He attended Pennfield School and graduated from Portsmouth Abbey School, both in Portsmouth. He went on to attend Merrimack College in Massachusetts.

Besides playing Charlie Kelly on the hit FX television series It's Always Sunny in Philadelphia, he is also the show's executive producer and one of its writers. He has also appeared on several other television shows such as Third Watch, Law & Order, and Reno 911!.

He appeared in New Line Cinema's Horrible Bosses in July 2011, opposite Jason Bateman, Jason Sudeikis, Kevin Spacey, Jennifer Aniston, Colin Farrell, and Jamie Foxx. He also had a role in the 2010 film Going the Distance, alongside Justin Long, Jason Sudeikis, and Drew Barrymore. In 2013 he will be appearing in Guillermo Del Toro's film Pacific Rim.

Robert Dale "Rob" McElhenney (pronounced /ˈmækɨl.hɛni/; born April 14, 1977) is an American film and television actor best known for his role as Mac on the FX TV series It's Always Sunny in Philadelphia. He is also credited as creator, developer, and executive producer of the show, which has also provided McElhenney with writing and directing credits on various episodes.

McElhenney was born in Philadelphia, Pennsylvania. McElhenney attended Waldron Mercy Academy for grade school. He then went on to attend Saint Joseph's Preparatory School in urban Philadelphia for high school.

Rob McElhenney made his film debut with a bit part in Alan J. Pakula's The Devil's Own and followed that up with bit parts in A Civil Action, Wonder Boys, and Thirteen Conversations About One Thing. He later had more substantial parts in Latter Days and The Tollbooth. McElhenney played a small role in the eighth season Law & Order episode "Thrill".

He was still waiting tables between acting assignments in 2004, when his manager and agent presented McElhenney's idea for a sitcom to the FX cable network, which received it warmly. McElhenney said that 50 weeks of each year are consumed by acting, producing, and writing for the show, but he did find time to appear in the third season of Lost as Aldo in the episode, "Not in Portland". This was a result of McElhenney meeting Lost co-creator and executive producer Damon Lindelof, who is a fan of It's Always Sunny in Philadelphia. McElhenney continued the role in Lost, featured again in the sixth season for a single episode (episode 2).