Before It's Always Sunny in Philadelphia became the cultural phenomenon it is today, the show's creators weren't sure they would even make it to a second season. Producers warned them that if they didn't put on an A-lister, they'd be out of a job. Reluctantly, show creators and stars Rob Mac, Charlie Day, and Glenn Howerton added industry legend Danny DeVito to the main cast (arguably, the smartest decision this rag-tag group could have made).