Pearl Slaghoople is the red-haired cavewoman mother of Wilma Slaghoople Flintsone and mother-in-law of Fred Flintstone. The character was never given a first name in the original run of the series, but the various movie attempts and the later animated series provided her with the first name Pearl.
Though no specific age is ever given, Mrs. Slaghoople appears to be middle-aged. She is implied to be a widow, referring to her husband (and Wilma's father) exclusively in the past tense, but as befits a 1960s animated series intended for family viewing, Mr. Slaghoople is never explicitly revealed as dead. Her conversations with Wilma suggest that Wilma is an only child and Mrs. Slaghoople's only living relative left, giving her a frequently invasive interest in Wilma's life and an exaggerated distaste for Fred's inability to provide her daughter with a more luxurious and economically secure life.
A loud, comedically bitter woman who complains about her past almost as much as she complains about Wilma's present, Mrs. Slaghoople had always hoped to marry her daughter off to a rich family friend, thereby ensuring that Wilma would never go through the financial struggles Mrs. Slaghoople had faced in her own young adulthood and marraige. As a consequence, she has never approved of Fred as a son-in-law, bonding with him only once and then only over their shared devotion to Pebbles.
Mrs. Slaghoople and Fred Flintstone are quite similar in many ways. They both are loud, stubborn, prideful, easily riled, often bitter about their money worries and often dreaming of wealth and how much they could use it to improve Wilma's life, and completely devoted to Wilma (and to Pebbles once she comes along); one episode implies that the late Mr. Slaghoople had been the same way, though others imply he may have been quiet and passive. Several episodes imply that one of the things that Wilma loves about Fred is that he reminds her of her parents.
In the original series continuity, Wilma and Betty met Fred and Barney while working at a ritzy motel during one of their first summers after graduating from high school; at the time, Fred lied that he was rich directly to Wilma and indirectly to Mrs. Slaghoople, thereby setting up the conflict about his earning power that has plagued Fred's relationship with Mrs. Slaghoople ever after. In later continuities, when the four of them have known each other since children, Mrs. Slaghoople makes almost no appearances of any consequence. The Flintstones series have never really attempted to follow a single continuity.
In that episode, Mrs. Slaghoople revealed that theirs had been a financially poor family and that she had loved her husband but always resented his inability to bring in a greater income. This seems to have much to do with her distaste for Fred as the husband of her only daughter.
Like all the "cave people" of The Flintstones series, Mrs. Slaghoople easily performs feats of strength that are superhuman by modern standards, including lifting stone slabs twice her size overhead, and she would appear to have a low level of invulnerability compared to a modern human being. (This greater strength and toughness has been vaguely alluded to the few times that the Flintstones and Rubbles have travelled into the future to the modern day or even past that to the retrofuturistic days of the Jetsons).