It's strange to think that a series like It's Always Sunny in Philadelphia has any secrets to keep. The Gang may be the five worst people on Earth, but they're usually brutally honest with each other and with viewers. Surprisingly, there are actually a few mysteries still floating around their world. And a big one relates to the identity of a recurring character known only as the Waitress who has yet to be named 14 seasons into the series.
The core members of the Gang have known each other for a long time. Dennis and Dee are siblings, but they got to know Charlie and Mac in school. Despite what Dennis likes to believe, they were all outcasts and found a twisted, toxic support system with each other. Frank, the man Dennis and Dee long believed to be their father, joined the Gang at the beginning of Season 2 and has become integral to its dysfunction.
But in addition to Dennis, Dee, Mac, and Charlie, another regular character made her debut in Season 1, Episode 1. While none of them seem to remember this, the Waitress also went to high school with the members of the Gang. They were incredibly surprised to see her show up at their high school reunion in Season 7, Episodes 12 and 13. But that's par for the course in their treatment of her.
One of the show's strongest running gags is the fact that no one in the Gang seems to have any idea what the Waitress's real name is. This includes Charlie, who stalked her for many years, possibly going all the way back to high school. Even he has never spoken her name and only refers to her as the Waitress. But that's likely because everyone else in the Gang gets confused if they hear her name used in any context.
While viewers have never heard her name used, it's come up in rather sneaky circumstances. In Season 8, Episode 4, Charlie finally let go of his obsession with the Waitress and moved on to someone else. Well, that's how it looked from the outside. It turned out that it was all a gambit on his part to make the Waitress miss him and crave his presence.
When Charlie wasn't helping her, the Waitress started pestering Dennis, who she had a crush on and had slept with. Dennis hated this for two reasons. One, he did not like to help people. And two, he did not like the Waitress. At one point, she called him and introduced herself using her real name. Dennis was confused by this as he did not remember her name, despite knowing her for decades and sleeping with her on at least one occasion.
Viewers only heard the call from Dennis' side and did not hear the Waitress speak her own name. As cruel a tease as it was, this was the closest fans have gotten to learning the truth. At this point, it has become a testament to the cruelty of this group of people. They see her as a disposable person who isn't even worthy of having a name. That being said, they still treat the Waitress better than Rickety Cricket.