Peggy's cousins Zemus Wanker and Ida Mae Wanker (played by Bobcat Goldthwait and Linda Blair) drop off their son and leave him behind for the Bundys to take care of. He appeared on the seventh season of Married with Children in a handful of episodes, then disappeared without any explanation other than a quick mention by the D'Arcys that he showed up in their house and won't leave. They claim they want to rename him, and possibly begin taking care of him, but that's the last time he is referred to.
He was an extremely unpopular character with the fans. However, in season eight, in the episode "Kelly Knows Something", Kelly is studying for a trivia show. As she learns new information, you visually see her forgetting other things. One thing that "pops out of her head" is an image of Seven. There is a scene where a carton of milk is held up at the Bundy's breakfast table and a picture of Seven is shown on the carton under the heading "Missing" but the Bundys don't seem to notice, or care. The milk carton with the picture of Seven under the "Missing" heading was also prominently featured in the epsisode "Ride Scare".
For a large number of fans, the introduction of Seven was where the series, at the very least, came perilously close to "jumping the shark", a reference to a Happy Days episode where that activity happened and subsequent episodes went downhill. Seven also represented other TV tropes, such as "Cousin Oliver", referencing a Brady Bunch concept where a younger, cuter character appears with little backstory in order to boost ratings, as well as "Chuck Cunningham Syndrome", another Happy Days reference where a main cast character disappears from the show with no explanation whatsoever.
Seven was played by former child actor turned grown-up actor Shane Sweet.