Bearcub's Grandmother is a violent, bitter Northern Wanderer and Slave aboard the American Dream 2.
In the books
In How to Ride a Dragon's Storm, She places a curse on Norbert's ship and warns that if any Viking falls into the Slave Hatch, she will kill them and eat them.
Later, Hiccup accidentally falls into the Slave Hatch during one of Norbert's tantrums. The Wanderers try to kill him, but Hiccup commmunicates with them in dragonese, stating that he can help set them free. The Grandmother bitterly doubts this, but seeing there is no choice, she agrees, but in order for Hiccup to keep that promise, she gives him the Slavemark.
In the middle of the book, Hiccup and the others drug Norbert and the Hysterics with intoxicating Dragon nip. They set the slaves free in life boats, but when the ship was attacked by the Leviathorgan, it seemed the slaves abandoned them, as they sail away. At the end of the book, it was revealed, that they left so they that can get reinforcements, the Grandmother thanks Hiccup, and they leave for home.