Gak Shadowski is the older sister of Ook Shadowski.
Gak first appears when Chief Goppernopper attempts to arrest her brother and his best friend Gluk Jones. Goppernopper falls in love with her and threatens to arrest Ook if she doesn't marry him. Ook and Gluk stop the wedding with Mog-Mog and get rid of Goppernopper. She isn't in the middle of the book, but after Ook and Gluk save Caveland and wipe out the Goppernopper bloodline, she appears at Ook and Lan's wedding.