Karen Griffin is Peter Griffin's sister, a wrestler who performs under the name of "Heavy Flo", and the main antagonist of the episode "Peter's Sister" of the "Family Guy" TV series.
When she drops in to visit for Thanksgiving. Meg discovers that she treats Peter the same way that he treats her. Although amused at first, she realizes that Karen takes things too far and decides to work with Peter to even the odds.
Karen's physical and emotional abusive treatment of Peter is very much the same as the way Peter treats Meg (possibly because Meg is somewhat similar in appearance to Karen) and a clear explanation of Peter's own abusive behavior, not only to Meg but to everyone Peter disregards in his unpredictable escapades and mayhem, which so very often cause someone some form of pain and/or misery. In other words, Karen is somewhat responsible for her brother being the man he is today.