It's Always Sunny In Philadelphia's theme “Temptation Sensation” is an iconic part of the show - but its inclusion was a happy accident. It's almost bizarre to think It's Always Sunny In Philadephia is one of the longest-running live-action sitcoms in TV history. The show is a dark, bleak look into the sad lives of the Paddy's Pub gang, who are generally nasty and selfish people. That said, the series is also hilarious and has only gotten better since it debuted way back in 2005.
It's Always Sunny In Philadephia's special ingredient is the cast, including Glenn Howerton (Dennis), Kaitlin Olson (Dee), Danny DeVito (Frank), Rob McElhenney (Mac), and Charlie Day (Charlie). The show has lasted for fourteen seasons and counting, with the characters themselves showing remarkably little in the way of personal growth or wisdom. That said, the season 13 finale "Mac Finds His Pride" drew acclaim for tackling Mac's struggle to find his place as a gay man, and ending with a surprisingly moving dance scene.
Both the creators and FXX seem happy to keep It's Always Sunny In Philadelphia going, so fans shouldn't have to worry about it coming to an end anytime soon. One of the most familiar elements of the show is the theme that plays over the opening credits, which is a jaunty, upbeat piece of music that is usually totally at odds with the darkness of It's Always Sunny In Philadelphia. A recurring gag involves a member of the gang saying something in the intro scene, only for the episode's title card to appear and completely contradict their last line while "Temptation Sensation" starts playing.
Like Curb Your Enthasistism's "Frolic" it's hard to imagine It's Always Sunny In Philadelphia without “Temptation Sensation,” but it almost wasn't used at all. Charlie Day once revealed in an EW interview that while looking through public domain songs to use, they were leaning towards "Off Broadway" by Werner Tautz as the theme, but John Landgraf - the president of FX - preferred "Temptation Sensation" by Heinz Kiessling and insisted they use it.
This turned out to be an inspired decision, despite being motivated by the fact it was a public domain song. "Off Broadway" is another key theme used on the show, which has turned using stock music into an art form. It's Always Sunny In Philadelphia has gifted the world with some memorable original songs too, including "The Dayman" - which is part of Charlie's infamous musical "The Nightman Cometh" - and "I Like Paddy's Pub."