The Duke ("Master" as the Cheshire Cat calls him) is a mass of distortions created by Wonderland. It first appears in Chapter 4, and is the only named character that did not appear in the original story.
"The residents of Wonderland don't know how to look back at the past. What's broken stays broken, they don't know how to fix it. So an existence that swallows these Regrets and abandoned pasts is necessary. The abandoned story is ignored, the pages, thrown away. The torn up, scrawled-on paper. The ink stained scraps of paper. The Duke is obsessed with Alice. Usually, it quietly collects waste in Wonderland. However, when it becomes unable to deal with the waste it holds, it begins to want Alice for itself, and it goes berserk."