Gibbon is the future son of Charlie and the supposed patriarch of the future Pup Kingdom. He made his first appearance in a vision that his mother experienced in "Daddy-Daughter Card Wars". He is a crossbreed of rainicorn, dog, shape-shifter, and some unspecified species.
He appears at an older age in the opening of the series finale "Come Along With Me". At some point, as shown in the intro to the series finale, one of Gibbon's eyes was replaced by one of the Ice Thing's gems. This has been confirmed by Steve Wolfhard to have granted him immortality and control over "pink ice". Apparently he is an unmerciful ruler and is greatly hated by Shermy and Beth.