The Old Hag is an unnamed character that appears in "Sister Smurf". She is an evil (presumably homeless) woman that traps Smurfette and Laura in her house.
In the story, Smurfette befriends Laura when no Smurf wants to pay attention to her new dress (with Laura experiencing being mistreated by her older brothers). When the two run off and hear Laura's brothers coming back, they run off and go to a house in the middle of the forest.
Soon, an old hag finds the two girls and traps them in the house, which was revealed to be hers, forcing them to do chores for her personal amusement. While the two hide in the cellar, Laura's brothers and a group of Smurfs team up to find them. The hag is defeated by the Smurfs pelting the woman with peas and the dog eating her roasted bird to distract her, leaving her to get distracted and yells at her dog as the Smurfs escape with the humans.